Examples of Math Problems: let cos x = 1/sqrt(10) with x in quadrant IV. find cos 2x.

Thursday, January 1, 2015

let cos x = 1/sqrt(10) with x in quadrant IV. find cos 2x.

Using a double angle identity:

cos%282x%29=2cos%28x%29%5E2-1

so we can write:

2%281%2Fsqrt%2810%29%29%5E2-1=1%2F5-1=-4%2F5

but cosine is positive in Quad IV, so...

x=4%2F5

x=4%2F5

No comments:

Subscribe to: Post Comments (Atom)