Question

$cos frac{x}{8} = - frac{ sqrt{2}}{2}$

Answer 1

cos(x/8)=-√2/2
cos π/4=√2/2
cos 3π/4=-√2/2, cos 5π/4=-√2/2
a)x/8=3π/4 +2k.π
   x=6π+16k.π=2π(3+8k),k∈Z
b)x/8=5π/4+2k.π
   x=10π+16k.π=2π(5+8k),k∈Z