Need Math Help?

[ExCeL 52]

Wrong. Nothing times nothing, is anything but zero.

Think about it, if you have no nothings, you have something. Double negative.

Oh man, your cool.

 

[AltF4]

No, lol, it doesn't work like that, Face. We are not talking about an object called a "nothing". We are talking quantities of arbitrary units.

You don't have "no nothings". You have "zero groups, each with zero objects in those groups".

 

[DtJ Jungle]

ahahahaha raep son

 

[meta master]

A logarithm is the reverse of an exponent. (NOT the same as a root)

The logarithm of a number with respect to the base is the power you have to raise the base by in order to get the number.

For example:

2^3 = 8
"2 to the power of 3 equals 8"
Then by defintion of a logarithm:
log2 (8) = 3
Meaning, "if you take the log of 8 with respect to 2, you get a power of 3"

Suppose you wanted to know,
"10 to the what power equals 500"?
or
10^(x) = 500

Now 10^2 = 100 and 10^3 = 1000, so x won't be a nice round number, but it must exist, and it will be somewhere between 2 and 3.

Here is where you would use the log function:

log10 (500) = x

You're not supposed to know this number off the top of your head, but if you use a calculator, you will get

log10 (500) = 2.699

This means that 10^(2.699) = 500

one more thing about logs is that on your calc (if you have a ti 83/84), its log (base 10). to get an answer, for say 2^x = 8. you do log2 (8). do the formula (log answer)/(log base). thus log8/log2. that should give you three (check it with various numbers on your calc)

 

[ConnorTheKid]

hey, so I have a problem about ratios and I'm having a really hard time with finding scale factors. mind helping me out?

1. The ratio of one side of triangle ABC is the corresponding side of similar triangle DEF is 3:5. The perimeter of triangle DEF is 48 inches. What is the perimeter of triangle ABC?

 

[DtJ Jungle]

set up the proportion

3/5=x/48

solve for x

 

[Face124]

Oh man, your cool.

Eh... Peach is a amazing character. Her defensive game is the best in Brawl by far.

I admit though, Altf4 sort of killed me

 

[Lemonwater]

Math = Worst subject ever

That is all.

I don't get people who can like math...

 

[1048576]

Math is unique in that studying has almost no correlation with performance. The people who like math are probably really good at it, and thanks to math, they can get a high-powered job and be lazy in school. I don't know if that applies to any of you, and I'm not saying it does, but it applies to three of my firends, which seems significant.

 

[OlimarFan]

Math = Worst subject ever

That is all.

I don't get people who can like math...

I don't get people who doesn't like maths!

lol maths is awesome

 

[Ravener]

Math = Worst subject ever

That is all.

I don't get people who can like math...

Maths is awesome its heaps better then the likes of literater and politics.

 

[GreenKirby]

So I just took a test in Mathematical logic and I did pretty well. Though I'm wondering if did this one problem right. Maybe you guys can help.

The problem was using the contrapositive method to prove if either x or y is irrational, then x+y is irrational.

So basically here's what I did:

Since the contrapositive of "p the q "is "~q then ~p" ,make x+y rational and assume both x and y are irrational

Use integers q,r, and s to make x+y = (q+r)/s where s=/=0

Then solving for both x and y, x= q/r and y = r/s.

Thus both x and y are rational though it was assumed both was irrational.

Thus x or y must be irrational so that x+y can be irrational.

is it right?

 

[plasmawisp6633]

I need help approximating the area of a circle using Isosceles triangles. The circle is cut like a pizza with N triangles.

It is stated that S(N) is the sum of the area of N identical triangles inside the circle (each with side/radius of R). The angle between each triangle is 2(pi)/N.

For the first part of the problem I have to show that S(N) = (1/2)NR^2 * sin[2(pi)/N]

For the second part I have to explain, using the limit as N approaches infinity of S(N), why it results in the normal formula for the area of a circle (A = (pi)R^2).

If anyone understood that, please help me. This is the last question for an assignment that's for a quiz grade. Thx.

 

[Teczer0]

Can anyone help me with Electomagnetic Fields?



I need help with Physics too...

Should I be asking these here... I don't know whether to put this here or the science topic .

 

[thesage]

Just memorize all the equations in physics.

 

[cF=)]

Just memorize all the equations in physics.

Works in high school, fails beyond that. The level of understanding required by my exams go way further than the equations seen in class by a good margin.

 

[AltF4]

So I just took a test in Mathematical logic and I did pretty well. Though I'm wondering if did this one problem right. Maybe you guys can help.

The problem was using the contrapositive method to prove if either x or y is irrational, then x+y is irrational.

So basically here's what I did:

Since the contrapositive of "p the q "is "~q then ~p" ,make x+y rational and assume both x and y are irrational

Use integers q,r, and s to make x+y = (q+r)/s where s=/=0

Then solving for both x and y, x= q/r and y = r/s.

Thus both x and y are rational though it was assumed both was irrational.

Thus x or y must be irrational so that x+y can be irrational.

is it right?

Sounds right. But it might be good form to make perfectly clear what is P and what is Q when doing the negations and contrapositives. So just say:

P = x or y is irrational
Q = (x+y) is irrational
not P = x and y are rational
not Q = (x+y) is rational

Then you say you will use the contrapositive:
not P implies not Q

Now you are doing a proof by contradiction. You will state the negation of "not P implies not Q" and show that it is contradictory. Thus, the contrapositive is true, thus the original statement is true.

You did this, but it would be helpful for a grader if you spelled it out more explicitly.

 

[plasmawisp6633]

I need help approximating the area of a circle using Isosceles triangles. The circle is cut like a pizza with N triangles.

It is stated that S(N) is the sum of the area of N identical triangles inside the circle (each with side/radius of R). The angle between each triangle is 2(pi)/N.

For the first part of the problem I have to show that S(N) = (1/2)NR^2 * sin[2(pi)/N]

For the second part I have to explain, using the limit as N approaches infinity of S(N), why it results in the normal formula for the area of a circle (A = (pi)R^2).

If anyone understood that, please help me. This is the last question for an assignment that's for a quiz grade. Thx.

I'm still having trouble. Please, help.

 

[Levitas]

A=1/2*a*p where a is the apothem (wikipedia) and p is the perimeter.

the first is just a rewritten form of that formula.

For the second part, the perimeter approaches the circumference of the circle as N goes to infinity, so we have p = 2*pi*r

Since the apothem gets closer and closer to the edge of the circle, a = r when N goes to infinity.

through substitution, we get A=pi*r^2

 

[plasmawisp6633]

A=1/2*a*p where a is the apothem (wikipedia) and p is the perimeter.

the first is just a rewritten form of that formula.

For the second part, the perimeter approaches the circumference of the circle as N goes to infinity, so we have p = 2*pi*r

Since the apothem gets closer and closer to the edge of the circle, a = r when N goes to infinity.

through substitution, we get A=pi*r^2

Still stuck on the second part. I'm trying to get the limit of (1/2)NR^2 * sin(2pi/N) to equal (pi)R^2 using L'hopital's Rule, but I'm getting nonsense. Any more help?

*note, the only variables I can use here are R and N*

 

[Levitas]

1/2*N*sin(2pi/N) should go to pi as N goes to infinity.

I get the right answer, just use l'hopital's rule for the top being 1/2*sin(stuff) and the bottom being 1/N.

note that the limit of sin(stuff/N) goes to 0 as N goes to infinity, and cos goes to 1 and chain rule that crap.

 

[¯\_S.(ツ).L.I.D._/¯]

Guys can anyone explain to me what Trig is useful for in real life? I just started the basics (sin, cos, tan, etc) in my Honors Geometry Class (I'm only an 8th grader don't flame me lol) and it's boring me a lot. It's not that I don't get it I just don't understand what it can help you with really... And I wasn't paying attention but when I do sin A for example and the ratio is 3/5 and then I hit sin on my calculator for 3/5, is the number that shows up the length of the side or what? I probably should've payed attention... w/e though.

 

[Pr0phetic]

Well if your aspiring to be an Architect, it may help. Otherwise, it gets you your grade and credit, credit allows you to graduate, and that allows your career. woot!

Oh, and the ratio is a side to another side, whether it be leg 1, leg 2, or the hyp. 3/5 could be leg 1: leg 2 or leg 1: hyp or leg 2: hyp, they have to specify.
lol later S.O.L.I.D. :-D

 

[AltF4]

Ah, another "Where the hell am I ever going to use this?!" question, huh?

The short answer is that you will use it. You really will. The long answer is... well... long.

It depends on your future career path. If you plan on being any kind of Engineer or Scientist, then trig is an absolute must.

But in high school, you should concentrate on not limiting yourself. You should be still trying to figure out what you want to do, and not limiting what you CAN do. If you don't go through trig, you are shutting a major door of opportunity on yourself.

 

[plasmawisp6633]

1/2*N*sin(2pi/N) should go to pi as N goes to infinity.

I get the right answer, just use l'hopital's rule for the top being 1/2*sin(stuff) and the bottom being 1/N.

note that the limit of sin(stuff/N) goes to 0 as N goes to infinity, and cos goes to 1 and chain rule that crap.

OMG it worked out. Thanks a lot.

 

[Death]

Geometric sequences? WTF??

Determine the value of x such that x+2, 2x + 3 and 4X + 3 are consecutive terms in a geometric sequence.

So far I have:

Tn (general term) = (x+2)(5/2)^n-1 Where do I go from here

Determine the value of x such that x - 2, -2 - x and x +10 are consecutive terms in an arithmetic sequence. Then a geometric sequence.

If T7 = 2196 and T5 = 324, find T3. ?????

 

[Frown]

I need a question/problem/riddle related to math, which may seem hard but makes you think "Why didn't I realize that?" when you hear the answer.

plz

 

[1048576]

Under what counting system does 100 = 60, 99 > 89, 105 < 87, and 1000 > 203

A microwave

 

[AltF4]

I need a question/problem/riddle related to math, which may seem hard but makes you think "Why didn't I realize that?" when you hear the answer.

plz

A joke:

A riddle (taken from mathwarehouse.com)

Question: How can you add eight 8's to get the number 1,000? (only use addition)


Answer:

Spoiler

888 +88 +8 +8 +8 =1,000

Another riddle (more advanced, perhaps. But not taken from anywhere):

The Infinite Hotel

The Infinite Hotel has an infinite number of rooms. Each room is numbered, 1, 2, 3, 4... etc...

It's a busy Saturday night, and would you know it? The Infinite Hotel is booked up. Full. Every single room is taken.

But just then, an infinite number of people walk into the lobby and want rooms! How can the hotel fit this new infinite group of people into the already booked Infinite Hotel?


Answer:

Spoiler

Have everyone already in the hotel to double their room number, and move to that room. So the people in room 3 will move to room 6, the people in room 6 will move to room 12, etc...

Now only the even room numbers are taken! Every odd numbered room is open. The new group of infinite people can take the odd numbered rooms!

 

[Frown]

Sloving equation by one Blodnie

Thanks. I'll check how my math teacher reacts.

 

[Kevin]

Quick question about determinants. If a 5x5 matrix A exists, and det(A)=-2
What would det(3A) equal?

What if it was a 6x6 matrix or 4x4?

what about det(2(A^-1[inverse]))

I did experimenting with a 3x3 matrix and found it to be 3^3=27 times -2, but am still unsure of higher matrices

 

[Fly_Amanita]

How much linear algebra do you already know? Do you know that det(AB)=det(A)det(B) for nxn matrices A and B, or that if you multiply one row of some matrix A by some scalar r, then the determinant of the new matrix is rdet(A)? If you know the former, and if A is some nxn matrix, think of 3A as the following product: the nxn matrix that is 3 on the main diagonal and zero everywhere else (i.e. 3 times the identity matrix) times A. If you know the latter, think of 3A as A with each row multiplied 3. I have more info in the spoiler tags below if you want to see more:

Spoiler

If you have an nxn matrix A and some scalar r, det(rA)=(r^n)det(A). To see this, let B be the nxn matrix that is r on the main diagonal and zero everywhere else. det(rA)=det(BA)=det(B)det(A). det(B) will just be r^n, since it is the product of the n r's on the main diagonal.

Hopefully this wasn't too incoherent, lol. I don't generally try helping people with math so I often have difficulty explaining things, but I've always heard that tutoring others is a great way of learning, so maybe I'll post here more often.

 

[Kevin]

Yeah I know a bit of the basics of linear algebra, barely anything on determinants though. I'm mainly looking into determinants right now and laws associated with it. I'm a pretty impatient person and I prefer to go straight to the solution and reverse-engineer the process.
So if a 5x5 matrix A exists, and det(A) = -2, then det(3A) would be (3^5)(-2)=-486? If so, gooooooooood cause that's what I did on a quiz recently (made up some matrices on spot and did a bunch of trial and error)

 

[forward]

Can someone explain to me what natural logs are? The "ln"

I've been doing problems with them and I just follow instructions but I don't understand what exactly the ln does or represents.

 

[Frown]

First off, do you know what e is?

There's a certain number that isn't affected by derivates, which is called e. It is about 2,71828183. e is always followed buy an exponent.

Log = 10^what
Ln = e^what

 

[Lixivium]

Can someone explain to me what natural logs are? The "ln"

I've been doing problems with them and I just follow instructions but I don't understand what exactly the ln does or represents.

You know what logs are right? If so skip the quoted section. If not...

From my earlier post:

A logarithm is the reverse of an exponent. (NOT the same as a root)

The logarithm of a number with respect to the base is the power you have to raise the base by in order to get the number.

For example:

2^3 = 8
"2 to the power of 3 equals 8"
Then by defintion of a logarithm:
log2 (8) = 3
Meaning, "if you take the log of 8 with respect to 2, you get a power of 3"

Suppose you wanted to know,
"10 to the what power equals 500"?
or
10^(x) = 500

Now 10^2 = 100 and 10^3 = 1000, so x won't be a nice round number, but it must exist, and it will be somewhere between 2 and 3.

Here is where you would use the log function:

log10 (500) = x

You're not supposed to know this number off the top of your head, but if you use a calculator, you will get

log10 (500) = 2.699

This means that 10^(2.699) = 500

Natural log just means log of the number e. As frown said, e is approximately 2.718..., but like pi, e is an irrational number that keeps going on forever after the decimal point.

 

[cman]

Does anyone know how to intergrate (x^2)/(1+x^5)? None of the methods i know work, or I am making a mistake somewhere. Either way, I need help with it

 

[1048576]

Are you sure you copied that right? My calculator is giving me a ridiculously large answer. I was thinking partial fractions, since the denominator splits into two quadratic factors and a linear factor, but that would be incredibly painful to try to solve.

 

[cman]

I'm sure that i copied it right. And how exactly does the denominator factor?

 

[Proud_Smash_N00b]

How do I integrate 1/sqrt(1-x^3)?

Do I use u-substitution to make u=x^(3/2) and then end up with an inverse sine funtion or do I make u=1-x^3 to end up with some ln function