another proof

[kaebun]

$\displaystyle cos(x)^4-sin(x)^4=cos(x)^2-sin(x)^2$ proof
i did the right side
$\displaystyle ((1+cos(2x)/2)-((1-cos2x)/2)$
$\displaystyle (1+cosx-1+cos2x)/2$
$\displaystyle (2cos2x)/2$
which is cos2x so basiclt i went a circle *fruturated* :x
ps sorry about asking so many questions i have a test tomarrow that id rather not fail

 

[skeeter]

factor the left side ...

cos^4(x) - sin^4(x) = [cos^2(x) - sin^2(x)]*[cos^2(x) + sin^2(x)]

do you remember what cos^2(x) + sin^2(x) equals?

 

[kaebun]

1

 

[kaebun]

wow i feel so dumb now thats so easy! thanks