2cos(2x + π/4) = – √2

2(cos2x cosπ/4 -sin2x sinπ/4 ))-√2

2(cos2x*√2/2 - sin2x*√2/2)-√2

2(√2cos2x/2 - √2sin2x/2)-√2

2*√2cos2x - √2sin2x/2 - √2

√2cos2x - √2sin2x - √2

Ответ: √2cos2x - √2sin2x - √2