Question

I have to evaluate cos (11pi/4) and sin (11pi/4)

Answer 1

I did it the way I thought was right and I ended up with (sqrt2/2, sqrt2,2) but it's cos needed to be negative. They said the reason was that 11pi/2 is 2pi + pi/2 + pi/4 but I don't really understand that.

Answer 2

(1/2)*2*sin (11pi/4) cos (11*pi/4)
=(1/2) sin 22pi/4

Answer 3

I still don't understand

Answer 4

2 sin x cos x=sin 2x use this first

Answer 5

now sin 11pi/2=sin (5pi+pi/2)

Answer 6

It still doesn't make sense to me, do I need to use a calculator to do this method? Because I can't on the exam

Answer 7

sin (4pi+pi+pi/2)=sin(pi+pi/2)

Answer 8

I'm honestly very lost

Answer 9

2pi is period of sin x that is sin(2pi+x)=sin x

Answer 10

Okay