# Math Help - I need help with this trig question...

1. ## I need help with this trig question...

Express as a single trig function:
how can I solve this question: 2cos^2 (pie/4)-1

THanks

2. Originally Posted by Ttops
Express as a single trig function:
how can I solve this question: 2cos^2 (pie/4)-1
double angle identity ...

$\cos(2x) = 2\cos^2{x} - 1$

fyi ...

this is pie

this is pi ...