5) -2cos 5x/2·sin 5x/2 = 1.

5) -2cos (5x/2)·sin (5x/2) = 1.

-sin(2*5x/2) = 1

-sin(5x) = 1

sin(5x) = -1

5x = -π/2 + 2πk, k ∈ Z

x = -π/10 + (2πk)/5, k ∈ Z

Ответ: x = -π/10 + (2πk)/5, k ∈ Z