# Math Help - compound/double angle formulas

1. ## compound/double angle formulas

If x is an acute angle such that tan2x = -24/7, find sinx and cosx.

help? thanks

2. Originally Posted by checkmarks
If x is an acute angle such that tan2x = -24/7, find sinx and cosx.

help? thanks
draw a right-triangle with acute angle 2x and opposite side 24 and adjacent side 7. use Pythagoras' theorem to find the hypotenuse.

then you will know that cos(2x) = (adjacent)/(hypotenuse)

then use the fact that $\cos 2x = 2 \cos^2 x - 1 = 1 - 2 \sin^2 x$ to find sin(x) and cos(x)

or you could solve.