Question

cos^-1(cos(9π/8)) without a calculator. I know the answer is 7π/8 but i have no idea how to arrive to that answer?

Answer 1

since the first and fourth quadrant has cos equal:
cos^-1 [ cos( 2π - 9π/8 ) ] = 7π/8

Answer 2

thats all?

Answer 3

Yep!

Answer 4

omg

Answer 5

so easy, thanks

Answer 6

Just visualize the unit circle, you'll figure out so many interesting facts ;)

Answer 7

i will!

Answer 8

:)