Ответ:

Б) 5sin2x - 2 sinx = 0

5 * 2sinxcosx - 2sinx = 0

10sinxcosx - 2sinx = 0

2sinx (5cosx -1) = 0 l : 2

sinx (5cosx -1) = 0

sinx = 0   x = pk

5cosx = 1    x = +- arccos (1/5) + 2pk

В) 2sinx + 5cosx = 0

2sinx = -5cosx l :cosx

2tgx = -5

tgx = - 5/2

x = arctg(-5/2) + pk  =  -arctg(5/2) + pk