olve for the interval [0, 2pi]. cos(x+ pi/4)+cos(x- pi/4)=1

Answer 1

that would be

cosx cos pi/4 - sinx sin pi/4 + cosx cos pi/4 + sinx sin pi/4 = 1
2cosx cos pi/4 = 1
√2 cosx = 1
cosx = 1/√2
x = pi/4, 7pi/4