Question

Найдите все решения уравнения: cos3x = cos12º

Answer 1

3-3cosx=2sin²x
3-3cosx=2(1-cos²x)
3-3cosx=2-2cos²x
3-3cosx-2+2cos²x=0
2cos²x-3cosx+1=0
cosx=y
2y²3yx+1=0

Answer 2

cos(3x)=cos(12)
12º=п/15+2пk
3x=п/15+2пk
x=п/45+2пk/3