could you help me on the following,

rcosxcosy * rsinxcosy

-rsinxsiny * sinxsiny

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- Feb 17th 2008, 01:57 PMheroicmultiplying trig functions
could you help me on the following,

rcosxcosy * rsinxcosy

-rsinxsiny * sinxsiny - Feb 17th 2008, 04:19 PMTwistedOne151
$\displaystyle r\cos{x}\cos{y}\cdot{r}\sin{x}\cos{y}=r^2\sin{x}\c os{x}\cos^2{y}$

$\displaystyle -r\sin{x}\sin{y}\cdot\sin{x}\sin{y}=-r\sin^2{x}\sin^2{y}$

-Kevin C. - Feb 18th 2008, 02:08 AMheroic
cheers mate.

now could you possibly help me simplify the following plz,

cosx[(r^2sinxcos^2y) - (r^2sinxcosxsin^2y)]

(-rsinx)[(rsin^2xcos^2y) - (-rsin^2xsin^2y)]

I'm sorry i'm askin for help, i kno this must be easy, but i can't do it. lol - Feb 18th 2008, 02:31 AMPeritus
try using the following identities:

$\displaystyle

\begin{gathered}

\cos ^2 x - \sin ^2 x = \cos 2x \hfill \\

2\sin x\cos x = \sin 2x \hfill \\

\sin ^2 x + \cos ^2 x = 1 \hfill \\

\end{gathered}

$

you might also take a look at this:

Table of Trigonometric Identities