Posted by **bee** on Monday, December 3, 2012 at 10:02pm.

when solving for all solutions how do I work out this problem: cos4(alpha)=cos2(alpha)

and when verifying each identity how do I complete this problem: sin (alpha/2)=sec alpha -1/2sin (alpha/2)sec alpha

- precal -
**Steve**, Monday, December 3, 2012 at 11:53pm
cos4x = cos2x

2cos^2(2x)-1 = cos2x

2cos^2(2x)-cos(2x)-1 = 1

(2cos2x+1)(cos2x-1) = 0

so, cos2x = -1/2 or 1

cos 2pi/3 = cos 4pi/3 = -1/2

cos 0 = 1

as for the identity, I get the feeling there's a typo, because secx appears twice on the right.

## Answer this Question

## Related Questions

- trig - FInd the exact value pf the 6 trig function of alpha Given: point (-2,-6...
- Trigonometry - Find the counterexample to shows that the equation sec (alpha) - ...
- trig - Please find sin (alpha/2) and cos (alpha/2) sec alpha = 3, -pi/2 < ...
- trig - express 20sin theta + 4 cos theta as R sin(theta + alpha) R sin(theta + ...
- Math ( Polynomial ) - This time three questions - 1. If (x^2 - 1 ) is a factor ...
- Math ( Polynomial ) - This time three questions - 1. If (x^2 - 1 ) is a factor ...
- Math - If alpha and beta are the zeros of the polynomial ax^2 + bx + c then ...
- trig - evaluate the following in exact form, where the angeles alpha and beta ...
- mathematics - If cos 9 alpha = sin alpha 9 alpha < 90 degree then 5 alpha =
- mathematics - If cos 9 alpha = sin alpha 9 alpha < 90 degree then 5 alpha =

More Related Questions