Author Topic: Another maths question (Read 7544 times)

Sigz · « **on:** May 05, 2011, 06:01:07 AM »

Studying for my maths exam, this was in the solution to the fourier series expansion question from last year's exam:

I can do everything else in the problem, but I don't understand how they from the 2nd step to the 3rd. Halp?

edit: OH GOD I WROTE MATHS NOT MATH AGGGGHHHHJDFJKFJASDKFJHSFKJ

Jamesman42 · « **Reply #1 on:** May 05, 2011, 06:11:33 AM »

Looks like a trig identity...let me check...

Jamesman42 · « **Reply #2 on:** May 05, 2011, 06:12:57 AM »

Yep, product to sum formula:

cos(u)sin(v) = (1/2)[sin(u + v) - sin(u - v)]

Which explains why the 2 on the outside of the integration went away as well.

Edit: Wrote the wrong identity

Sigz · « **Reply #3 on:** May 05, 2011, 06:34:16 AM »

Ah many thanks, I figured it was an identity I didn't know/remember.

Jamesman42 · « **Reply #4 on:** May 05, 2011, 06:40:56 AM »

Of course, baby. <3

But if you use the word "maths" again I'm gonna castrate you.

Sigz · « **Reply #5 on:** May 05, 2011, 06:47:34 AM »

hawt

MajorMatt · « **Reply #6 on:** May 05, 2011, 06:50:52 AM »

Quote from: Sigz on May 05, 2011, 06:01:07 AM

OH GOD I WROTE MATHS NOT MATH AGGGGHHHHJDFJKFJASDKFJHSFKJ

Then you wrote it correctly

Bonham · « **Reply #7 on:** May 05, 2011, 08:04:06 AM »

I hate trig identities with a burning passion...

dethklok09 · « **Reply #8 on:** May 05, 2011, 02:40:39 PM »

I got to the part with the "a" and I just gave up from there.

The Silent Cody · « **Reply #9 on:** May 05, 2011, 02:43:39 PM »

I hate math... $:\$

73109 · « **Reply #10 on:** May 05, 2011, 04:31:10 PM »

I hate Trig identities. Pain in my balls.

Jamesman42 · « **Reply #11 on:** May 05, 2011, 04:32:01 PM »

Why the hate? Because there are like 2,000 of them?

Implode · « **Reply #12 on:** May 05, 2011, 04:33:12 PM »

Quote from: Jamesman on May 05, 2011, 04:32:01 PM

Why the hate? Because there are like 2,000 of them?

Exactly.

73109 · « **Reply #13 on:** May 05, 2011, 04:57:01 PM »

Pretty much. They're just a pain in the balls.

Jamesman42 · « **Reply #14 on:** May 05, 2011, 05:16:38 PM »

I hear ya....taking a calc 3 test where you have to remember those rare identities was not fun. If I was a calc teacher, I'd let my students use a trig cheat sheet.

73109 · « **Reply #15 on:** May 05, 2011, 05:41:32 PM »

I used a trig cheat sheet. My teacher was cool. I also don't think many were rare.

Normal ones, inverse, half angle, double angle, adding, subtracting, multiplying...

rumborak · « **Reply #16 on:** May 05, 2011, 05:53:44 PM »

I hated those identities, until I learned about e^i*Phi stuff. After which all those identities were no longer needed.

rumborak

Jamesman42 · « **Reply #17 on:** May 05, 2011, 05:55:30 PM »

When I took calc, there were some that were used once over the course of all three calc classes, so there were a lot that were rarely used

73109 · « **Reply #18 on:** May 05, 2011, 05:58:03 PM »

I'm not looking forward to calc just because of these things. I adore algebra. The shit we are doing now, there is a good 3-4:1 ratio of variables to real numbers. That is when you know everything is right in the math world.

Jamesman42 · « **Reply #19 on:** May 05, 2011, 06:00:29 PM »

Calc is a whole new level. One way to think about it is that algebra is a very static system of math (still very useful of course)...but calculus takes algebra and extends it to have so many more applications (and with a lot more operations and rules).

Jamesman42 · « **Reply #20 on:** May 05, 2011, 06:00:54 PM »

Quote from: rumborak on May 05, 2011, 05:53:44 PM

I hated those identities, until I learned about e^i*Phi stuff. After which all those identities were no longer needed.

rumborak

What topic do you learn that concept in?

73109 · « **Reply #21 on:** May 05, 2011, 06:01:18 PM »

I just like variables.

The problems take forever, and you feel like Jesus once you're done.

bosk1 · « **Reply #22 on:** May 05, 2011, 06:04:28 PM »

I remember sitting in my calc 2 class one morning and the following thought hitting me: "When I was in algebra, I thought that once I took calculus, I know everything. I would be able to command numbers to bow down to me just be giving them a stern look. Now that I understand what my professor has just put on the board, I realize that although I aced my first semester of calc and am midway through my second, I know absolutely nothing."

wjc · « **Reply #23 on:** May 05, 2011, 07:58:25 PM »

Just to say that when we did e^(i*pi) etc in uni (school it was its own module of the four-unit course) we did it in the first weeks of Differential Calculus. Also that it is definitely maths.

Jamesman42 · « **Reply #24 on:** May 05, 2011, 08:00:41 PM »

Yeah, but rumborak was talking about e^(i*phi). Phi is something different than Pi. I know the whole e^(ix) = (cosx + i*sinx) from differential equations.

Ultimetalhead · « **Reply #25 on:** May 05, 2011, 08:19:30 PM »

Trig identities weren't too bad, but I missed the day where we went over the double-angle and half-angle identities, so I was well-fucked and far from home for a while.

The stuff we're doing in my pre-calc class right now is incredibly easy. Graphing rational functions is absolute cake compared to some of the shit we were put through in the first semester.

73109 · « **Reply #26 on:** May 05, 2011, 08:21:50 PM »

I love that shit. You mean piecewise functions and shit?

Jamesman42 · « **Reply #27 on:** May 05, 2011, 08:24:56 PM »

The last two posts are funny to read if you read them in the avatars' voices.

Are you both going onto calc at some point?

Ultimetalhead · « **Reply #28 on:** May 05, 2011, 08:26:38 PM »

I'm not sure. I'm going into music education, so I'm not sure if I'll need to move onto Calc or not for my general education stuff. If I don't have to, I probably won't. My schedule's going to be slammed as it is.

73109 · « **Reply #29 on:** May 05, 2011, 08:27:51 PM »

Yeah. I'm taking calc next year. I'm probably looking forward to that class more than any other.

wjc · « **Reply #30 on:** May 05, 2011, 08:57:12 PM »

Quote from: Jamesman on May 05, 2011, 08:00:41 PM

Yeah, but rumborak was talking about e^(i*phi). Phi is something different than Pi. I know the whole e^(ix) = (cosx + i*sinx) from differential equations.

Never heard of that. What is it?

Sigz · « **Reply #31 on:** May 06, 2011, 02:32:47 AM »

Quote from: wjc on May 05, 2011, 08:57:12 PM

Quote from: Jamesman on May 05, 2011, 08:00:41 PM
Yeah, but rumborak was talking about e^(i*phi). Phi is something different than Pi. I know the whole e^(ix) = (cosx + i*sinx) from differential equations.

Never heard of that. What is it?

https://en.wikipedia.org/wiki/Euler's_formula

wjc · « **Reply #32 on:** May 06, 2011, 06:07:59 AM »

Quote from: Sigz on May 06, 2011, 02:32:47 AM

Quote from: wjc on May 05, 2011, 08:57:12 PM
Quote from: Jamesman on May 05, 2011, 08:00:41 PM
Yeah, but rumborak was talking about e^(i*phi). Phi is something different than Pi. I know the whole e^(ix) = (cosx + i*sinx) from differential equations.

Never heard of that. What is it?

https://en.wikipedia.org/wiki/Euler's_formula

I meant as referring to e^(i*phi) which according to Jamesman is different to Euler's formula? eh

kári · « **Reply #33 on:** May 06, 2011, 03:47:32 PM »

Quote from: Jamesman on May 05, 2011, 08:00:41 PM

Yeah, but rumborak was talking about e^(i*phi). Phi is something different than Pi. I know the whole e^(ix) = (cosx + i*sinx) from differential equations.

Well yes but if you take Phi = Pi then you get that famous formula. I don't think you would learn about one but not the other...

Jamesman42 · « **Reply #34 on:** May 06, 2011, 03:54:00 PM »

I thought Phi was something different...or did rumborak make a typo?

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Author Topic: Another maths question (Read 7544 times)