1 а) (8+5)+7=13+7=20
б)(3+9)-6=12-6=6
в)14-(7+4)=14-11=3
г) (18-9)+5=9+5=14
д)(5+7)+(10-2)=12+8=20
2. 14-b=9
b= 14-9
b=5
ответ: b=5
c+8=13
c=13-8
c=5
ответ: с=5
<span>1)sinx+sin2x+sin3x+sin4x = (sinx+sin3x)+(sin2x+sin4x) =2sin2x× cosx+2sin3x× cosx =2cosx(sin2x+sin3x) =4sin(5x/2)× cos(x/2)× cosx</span>