Need Math Help?

[w!zard]

oohkay thanks!

 

[Proud_Smash_N00b]

What kind of specific math category is used in this problem mentioned earlier?:

Let f(x)= 1/(square root of 2x).
Calculate [f(x+h) - f(x)] / h and simplify

I have strange problems with these problems. What are they called? (And no, the explanation earlier didn't help me much)

It was under "rationalization" in the book I used lol

 

[Proud_Smash_N00b]

WORD PROBLEM HELP PLZ!!!

1. Write (sec x)^5 as (sec x)^2 * (some function of tan x)

Answer: +/- (sec x)^2 * (sqrt(1+ ((tan x)^2)))^3

I just wanna know how they got the +/-
---

2. Using the sum and difference formulas for sin and cos, derive the following results:
a. sum and difference formulas for tan
b. sum and difference formulas for cot

How do you do that?

 

[Doraki]

What's a word problem ?

 

[Proud_Smash_N00b]

What's a word problem ?

I used to have some but then I edited them out when I found out how I got it.. lol

 

[clowsui]

THis is more a Chemistry help problem >_> but it involves a lot of math

i need to somehow calculate the number of amu in a gram given the mass of a single atom of hydrogen and the gram molecular mass of hydrogen.

halp?

btw gmm = 1.01 g
# g H (1 atom) = 1.67 * 10^-24

 

[JLynn943]

this may be a stupid question, but what is a signed area?

we're doing determinants in linear alg/diff. eq., and the professor was talking about signed areas, where it would be possible to a have a negative area. i'm not sure i really get what he was talking about though. how would you end up with a negative area?

 

[AltF4]

JLynn943:

Area can be negative, sure. Don't think of area strictly in terms of physical objects. Area can represent lots of other things which make more sense as being negative.

For example...

Money. If you let a function, f(x), represent the rate someone is gaining (or losing) money, then you can find out the total amount of money they have by finding the "area under the curve" (integral).

But of course, depending on how the function goes, you might wind up with negative area. Does that make sense? Of course it does! That just means the person wound up in debt, is all.



Clowsui

I'm afraid my Chemistry-fu is fairly rusty, maybe someone else around here can help you with that one.


Proud Smash Noob

Are you certain you have your parenthesis correct in your "answer":

+/- (sec x)^2 * (sqrt(1+ ((tan x)^2)))^3

Because it would make more sense if the "+/-" were inside of the parentheses next to the secant.

 

[GoldShadow]

THis is more a Chemistry help problem >_> but it involves a lot of math

i need to somehow calculate the number of amu in a gram given the mass of a single atom of hydrogen and the gram molecular mass of hydrogen.

halp?

btw gmm = 1.01 g
# g H (1 atom) = 1.67 * 10^-24

I'll take this one!

Well, one amu is defined as approximately the mass of one proton (ie, one hydrogen atom) or one neutron. Therefore, the mass of one atom of H, which you're given as 1.67 * 10^-24 g, is one amu.

To find the number of amu in a gram, divide 1 gram by that number.

 

[M@v]

I'll be willing to help, although Ill probably have my hands full between college chem and college calculus >_>

 

[Wardub]

How would you find the derivative of 2^x, using the (f(x+h)-f(x)) / h definition. It's pretty easy to find that the derivative is ln(2)*2^x using chain rule.

But I can't seem to get it using difference quotients.

 

[#HBC | Mac]

some one help me find out how to do the integral of sin(x)cos(x)

 

[Lixivium]

some one help me find out how to do the integral of sin(x)cos(x)

You can do this with integration by parts (2 possible ways) or by a trig substitution. You get 3 separate answers, but they're all equivalent.

Spoiler

http://www.mathhelpforum.com/math-help/calculus/10998-integration-sinxcosx.html

 

[#HBC | Mac]

yea i was confused becuz my calculator and my text book gave two diff answers so i was just like wtf
thanx tho

 

[Tofu Beast]

I should put some of the questions from my SAT prep book in here...

Even my teacher is about to throw the book out the window because of some of the questions..

 

[__Lewis__]

Uhhh okay.
I'm struggling with Linear Programming, and I'm doing middle-of-the-road difficult maths.
I just need to know, given we have a worded problem to solve, how to discern what the variables are and the like. I know this is vague, but sorry. I don't have any specific, rather, I've got exams coming up and this is an area I struggle with.
Is there a website out there that has a good descriptions of math-related topics?

 

[ChileNess]

LOL as im a "child" i actually "good" at math but if i need help i will post here also Spanish posts will come in help

 

[The Executive]

Alt, would basic/intermediate calculus be out of the question?

 

[AltF4]

You mean, for you to ask a question about? No way! Ask away!

 

[The Executive]

Most awesome. I don't have one at the moment but inevitably there will be one. Good to know; I appreciate it.

Odds are if I do have a question it'll likely be about C++; do you answer those as well?

 

[AltF4]

I don't see why you can't ask programming questions as well.

 

[The Executive]

Awesome. I'm roughly six weeks into a C++ course and I'm coming along pretty well but most of my code is unnecessarily complicated. Half the time I write six lines when four would do; I'm just not calling the right functions. Prime example would be not using for loops when applicable instead of if which automatically wastes 2+ lines assuming everything is indented.

 

[Proud_Smash_N00b]

I'm a bit confused about limits
I know that all you do is plug in the value (c) where it says "x->c" but then I get confused during the times where you have to find the limit of (f(sin (x+h))-f(sin x)) / h. I remember doing a problem like this and I know you have to use the identity that makes it (sin x*cos h+cos x*sin h-sin x)/h but I don't know how to factor the top part. My teacher said that that was finding the derivative and I don't even know what that means

Is there a main goal in finding limits? Do you have to try to avoid getting infinity or something?

 

[MojoMan]

I just realized this thread existed I'm only in Junior High, but technically learning at a highschool math level. WE have the most ****ed up program in our school we have to work our way through a 16 chapter book all by ourselves, doing a set amount of problems for 30 minutes each night, and then take a test to get to the next chapter. If you don't finish by the end of they year, ur screwed. Only the kids who weren't lazy went onto Gemoetry last year. I am going to be asking questions all year. But I'm not sure if you want to answer such beginner questions (REALLY EASY ONES).

 

[1048576]

I can't explain how to do that particular problem (I'm not good at math, sorry) but I can explain the concept of a derivative. Remember when you took your first algebra course and you had to find the slope of a line? You did (y2-y1)/(x2-x1) to find the slope, correct? In calculus, you're trying to find the slope of an equation at a given point. You can estimate the slope by taking two points near the point for which you are trying to find the slope, and finding the slope of the line that connects the two points. (For example, suppose I wanted to find the slope of y = x^3 at (2,8). I don't know how to find the slope of a point, but I can estimate the slope by using (y2-y1)/(x2-x1) at the points (0,0) and (4,64).) I can get a better estimate by using the points (1,1) and (3,27). I can get an even better estimate at (1.99, 1.99^3) and (2.01, 2.01^3). As the change in the value of x approaches 0, the value of (y2-y1)/(x2-x1) approaches the slope at a given point, or the derivative.

I'll post this, even though it's sloppy and unhelpful, and refine it later, explaining why lim h->0 (f(x+h)-f(x))/(h) is the formal expression of a derivative for any value x, where h represents the change in x.

 

[Death]

Could someone please help me with these two questions? I don't understand them at all...

Derive the formula for uniform acceleration :

A) Delta D = v2*t - 1/2a*t^2

B) v2^2 = v1^2 +2a*delta D

HOW???

 

[Omis]

I'm only doing 9th grade math so this should be pretty easy, even though I dont have the exact words.

Basically the problem talks abouta pizzeria where the price of a pizza with a radius of six inches is eight dollars and the price of a pizza with a radius of twelve inches is thirty two dollars. The problem then asks for the price of a pizza with a radius of eleven inches, eighteen inches, and twenty four inches. The problem hevily talked about it being related to square roots and squares. When I asked for a hint the teacher wrote on my paper A over B equals C over D. I really have no clue what to do on the problem.

 

[io728]

If a train leaves seattle at 2:00 PM, and another train leaves Las Vegas at 2:30 AM, does any one give a crap?

Srry bout this I share an account with my kid.

 

[eighteenspikes]

Using the formula Area=pi*(radius squared) for circles, a six inch pizza has 36*pi square inches. If it costs 8 dollars, then the cost of one square inch of pizza is $8/36*pi. So for every 36*pi inches squared of pizza, it costs $8. You can use this ratio to figure out the cost of other sized pizzas:

Cost of a pizza / Radius Squared of the Pizza (pi*square inches) = $8/36pi*inches squared

Don't worry about actually putting in the value of pi. It'll cancel out later.
Multiplying both sides by the radius squared of the pizza gives you:

Cost of a pizza = ($8/36 pi*square inches) * Radius Squared of a Pizza pi*square inches

The pi*square inches will cancel each other out and you'll be left with the cost of the pizza, in dollars.

Using 11 inches as an example:

$8/36 pi*inches squared = $/(121 pi*inches squared)

$8 * (121 pi*inches squared)/(36 pi*inches squared) = $8 * 121 / 36 = $968/36, which rounds to about $26.89

hope that helps you, pizza guy

 

[1048576]

io: please don't spam this thread.

omis?: the price of the pizza is proportional to its area, (which you might expect, seeing as the cost to make a pizza is proportional to its area.) I don't know how you would arrive at that conclusion other than guess and check, but it's guessable. Anyway, the area of the pizza with radius=6 is pi*(6)^2 or 36pi. The area of the r=12 pizza is 144pi. The cost of the 36pi pizza is equal to its area times 2/(9pi). The same holds true for the 144pi pizza.

To find the price of a pizza with r = 11, just find the area times 2/9(pi), which is the same as 2*r^2/9. (242/9)

You can use the same expression to find the price of the othe pizzas. The answers are $72 and $128, if you need to check your work.

Edit: oop, I type slow.

Death: I can do part A.

d^2x/dt^2 = a (definition of acceleration)

integrate

dx/dt = at + v (velocity is the constant of integration. In other words, the rate of change of distance is equal to the acceleration times time + velocity)

integrate

x = at^2/2 + vt + x0

x-x0 = at^2/2 + vt (x-x0 is delta x)

 

[Lixivium]

The problem hevily talked about it being related to square roots and squares. When I asked for a hint the teacher wrote on my paper A over B equals C over D. I really have no clue what to do on the problem.

What, there's no square roots or A/B = C/D involved, you just need the area of a circle. You do know how to find the area of a circle right? A = pi * r squared.

 

[Omis]

What, there's no square roots or A/B = C/D involved, you just need the area of a circle. You do know how to find the area of a circle right? A = pi * r squared.

Here maybe If I explain more aobut what our class is doing right now it might help put my problem in perspective. This problem is part of study guide for our test. Right now we are doing recursive and closed definitions and functions. This problem was under the section for recursive and closed definitions.

 

[TPoint1BUA]

Could someone please help me with these two questions? I don't understand them at all...

Derive the formula for uniform acceleration :

A) Delta D = v2*t - 1/2a*t^2

B) v2^2 = v1^2 +2a*delta D

HOW???

Someone did part a already, but here's the proof using algebra.

d->delta
vf = final velocity
vi=v0=initial velocity
x=final position
x0=initial position
t=delta t

Here are your starting equations.
(1) vavg = dx/dt = (x-x0)/t
(2) vavg = (vf+vi)/2 (Literally just v average)
(3) a = dv/dt = (vf-vi)/t

Setting (1) and (2) equal, we get
(x-x0)/t = (vf+vi)/2, or
(4) x-x0 = t(vf+vi)/2

Multiplying both sides of (3) by t and then adding vi to both sides, we get
(5) vf = vi+at

Plugging (5) into (4), we get
x-x0 = t(vi+at+vi)/2
x=x0+t*2vi/2+t*at/2
(6) x = x0+v0t+1/2*at^2

For part B i will use roman numerals.

Multiplying equation (3) and (2) we get
a*vavg = (vf-vi)/t*(vf+vi)/2
(I) a*vavg = (vf^2-vi^2)/(2t)

Note: (If you have a=b and c=d, you can turn a=b into ac=bc and then replace the second c with d to find ac=bd)

Plugging (1) into (I) we get
a*(x-x0)/t= (vf^2-vi^2)/(2t)
2*a*(x-x0)=vf^2-vi^2
(II)vf^2=vi^2+2*a*(x-x0)

What, there's no square roots or A/B = C/D involved, you just need the area of a circle. You do know how to find the area of a circle right? A = pi * r squared.

Yes there is. The ratio of the costs of the pizza is the ratio of the areas. A/B=C/D certainly seems like ratios to me.

 

[SuperRacoon]

What is the ratio of radius to height that minimizes the surface area to volume ratio for a cone?

the volume of a cone is pi*r^2*h/3=V, the surface area is pi*r^2+pi*r*sqrt(r^2+h^2)=SA, I have no idea where to begin, on finding this ratio.

r/h that minimizes SA/V.

 

[Sgt Isaac]

Quick backstory: I'm a High school Sophmore and currently in Algebra II honors. The class seems VERY easy and I would like to learn some more higher level math instead of spending a whole week on Cramer's Rule I've gotten very good at mental math and can multiply 5 digit numbers in my head, do long division, memorize primes, etc... I just need some way to learn the concepts and postulates and written methods for college-level math courses.

Anyone know a website where I can learn higher level math like Calc, Analytical Geometry, vectors/tensors, and linear algebra? Or possibly recommend a book I could find at a Library.
Thanks in advance!

 

[nakedsnake]

Geometry question

I need help on 19 and 21
the two lines are parallel and cut by two traversals
19. Is looking for angle 6
21. Angle 8

 

[Omis]

I think Number 21 is 80 because half the line must be 180

 

[Lixivium]

I need help on 19 and 21
the two lines are parallel and cut by two traversals
19. Is looking for angle 6
21. Angle 8

19:

angle 9 = angle 5 = 155 (angles opposite a vertex are equal)
angle 5 + angle 3 = 180 (supplementary angles add up to 180)
angle 3 = angle 2 (alternate interior angles are equal)
angle 7 = 140 (given)

angle 2
= angle 3
= 180 - angle 5
= 180 - angle 9
= 180 - 155 = 25 degrees

angle 6 = 180 - angle 2 - angle 7
angle 6 = 180 - 140 - 25
angle 6 = 15 degrees

21:

angle 8 + angle 9 = 180 (supplementary angles)
angle 8
= 180 - angle 9
= 180 - 155
= 25 degrees

Notice that angle 8 = angle 2

 

[Death]

Okay my teacher is really pissing me off. He doesn't help us with ANYTHING. So i have to do this question without any help (if that makes sense )

A speeder passes a stationary police cruiser at t= 0s. The cruiser pursues the speeder as shown in the graph.

Ok so basically the graph continues until 17 seconds with the speeder going +30m/s the entire way. The police accelerates from 0m/s to +40m/s in 10 seconds and then maintains that speed until the end of the chase/trip.

Now, I was asked to calculate the displacement for each vehicle at 10s which turns out to be 300m, and 200m (the speeder is 300m). So they are 100m apart.

When will the police cruiser pass the speeder??

I got the answer of 20s which is correct by figuring out the displacement of both vechicles every seconds or so after the graph ends (at 17s). But my teacher wants me to either solve the problem graphically or algebraeically.

WTF?? and how do I do this? Can you use any formulas???

 

[marthanoob]

A plane flying with a speed of 300km/hr passes over me 1km over my head. Immediately after passing over my head, it then flies at an angle of 30 degrees maintaining the same speed. At what rate is the distance between me and the plane increasing after one minute?