20.
1) sin(α-3π) =sin(-(3π-α))= -sin(2π+(π-α))= -sin(π-α)= -sinα
2) cos(-π/2 +α)=cos(-(π/2-α))=cos(π/2-α)=sinα
3) sin(α-π)=sin(-(π-α))= -sin(π-α)= -sinα
= -2sinα - sinα = -3sinα = 0.6
-5sinα -5sinα
Ответ: 0,6
21.
1) 1 - 1 = 5a-4-(5a+4) = 5a-4-5a-4 = -16
5a+4 5a-4 (5a+4)(5a-4) 25a²-16 25a² -16
2) (25a² -16) * -16 = -16
25a² -16
Ответ: -16