Question

решите урвниние (cos2x+cosп÷4)(cos2x+4)=0

Answer 1

cos2x = -cos(π/4) либо cos2x = -4, но cos2x > -1, поэтому только 
cos2x = -cos(π/4)
cos2x = -√2 / 2
cosx = -√2 / 4
x = +-arccos(-√2/4) + 2πn, n ∈ Z