Posted: 10/25/2010 5:25:28 PM EDT
|
cos(3x)=cos^3(x)-3sin^2(x)cos(x) I got to: cos(x) * (cos^2(x)-3sin^2(x)) Now I'm stumped. Stupid 3! |
|
Quoted: So what about this?Quoted: Quoted: Work the left side of the equation. Look into the double angle formulas for clues. I know what the double angle identity for cos(2x) is, but does it work the same way for triple or quadruple angle identities? I don't know. Yes. cos(3x) = cos^3(x)-3sin^2(x)cos(x) =cos(x) * (cos^2(x) - 3sin^2(x)) =cos(x) * (1-sin^2(x) -3(sin^2(x))) =cos(x) * (1-3*sin^2(x)+sin^2(x)) =cos(x) * (1-3) =cos(x) * (-3) =cos(-3x) =cos(3x) I fucking hate these identities. They seem to through algebra out the window. |
|
Quoted:
Hmm...this one is stumping me a little. I hate F-ing trig identities. Needless to say, Calculus isn't much fun either. -D2V I hate them too. Lowered my grade from an A to a B. But then I was trying to teach myself how to do them. My teacher hardly spoke any English which did not help. |
|
Quoted:
Quoted:
I do, but it doesn't seem to fit right.
cos(a + b) = cos(a)cos(b) – sin(a)sin(b) a=x b=2x cos(a+b) = cos (x+2x) = cos(3x) .... you see where this is going. I have to make cos(3x) = cos^3(x)-3sin^2(x)cos(x) yeah i dont think I had the right identity. you may have to use more than one identity to get there too. |
|
Quoted: Quoted: Hmm...this one is stumping me a little. I hate F-ing trig identities. Needless to say, Calculus isn't much fun either. -D2V I hate them too. Lowered my grade from an A to a B. But then I was trying to teach myself how to do them. My teacher hardly spoke any English which did not help. My professor barely speaks English and brags that he feels it's his job to confuse us by giving us trick questions. I hate this asshole. I really do. |
http://mathworld.wolfram.com/Multiple-AngleFormulas.htmlthis editor is broken. |
|
Quoted:
Quoted:
I do, but it doesn't seem to fit right.
cos(a + b) = cos(a)cos(b) – sin(a)sin(b) a=x b=2x cos(a+b) = cos (x+2x) = cos(3x) .... you see where this is going. I have to make cos(3x) = cos^3(x)-3sin^2(x)cos(x) Identities needed: Sum Difference, Double Angle, Double Angle. (Distribution and simplify.) Start left side as he suggested. Any more and you'll be given the answer. 
|