Cos(70+x)*cos(x-20) = 1/2

Question

Cos(70+x)*cos(x-20) = 1/2

Answer 1

1/2*(сos90+сos(2x+50))=1/2
cos(2x+50)=1
2x+50=180n
2x=-50+180n
x=25+90n,n∈z