Without using tables(calculators) find the numerical value of
Sin[Pi/8]^2 - Cos[3 (Pi/8)]^4
The Attempt at a Solution
I tried changing it to:
1-cos[pi/8]^2 - cos[3pi/8]^4 but have no idea where to go... its really got me scratching my head.
Any ideas? Any help is much appreciated, thank you.