1) sin2x=sinx
2sinx*cosx-sinx=0
sinx(2cosx-1)=0
sinx=0 или 2cosx-1=0
x=πn 2cosx=1
cosx=1/2
x= ±
2) -sin2x=cosx
2sinx*cosx+cosx=0
cosx(2sinx+1)=0
cosx=0 или 2sinx+1=0
x=π/2+πn 2sinx=-1
sinx=-1/2
x= 
1)18y-21=3y^2-42
18y - 21 - 3y^2 +42 = 0
-3y^2 +18y +21 = 0 / : 3
-y^2 + 6y +7 =0
D = b^2 - 4ac = 6^2 - 4*(-1) * 7 = 36+28 = 64
VD = V64 = 8
x1 = (-6+8)/2*(-1) = 2/-2 = -1
x2 = (-6-8)/2*(-1) = -14/-2 = 7
2)(x+8)(x+7)=0
раскроем скобки
x^2 + 7x +8x +56 = 0
x^2 + 15x + 56 = 0
D = b^2 - 4ac = 15^2 - 4*1*56 = 225 - 224 = 1
VD = V1 = 1
x1 = (-15+1)/2 = -14/2 = -7
x2 = (-15-1)/2 = -16/2 = - 8
3)10+8х=3x-5
10 + 8x - 3x +5 = 0
15 + 5x = 0
15 = -5x
x = -3
10 + 8*(-3) = 3*(-3) - 5
10 + (-24) = -9 - 5
10 - 24 = -9 - 5
- 14 = -14
