Question

If cos x=0.42 which of the following is
cos (x+12pi)
a) 0.042
b)0.04
c)0.54
d)0.42

Answer 1

cosine is periodic with period \(2\pi\) so
\[\cos(x)=\cos(x+2\pi)=\cos(x+4\pi)=\cos(x+6\pi)=...\]