3x^4 - 12x^2 = 0 0,7x^2 + 8x = 0 2x^2 + \frac{3}{4} x = 0

1. 3x²(x² -4) =0
3x² =0, x=0
x² -4=0, (x -2)(x +2)=0
x -2=0, x=2
x +2=0, x= -2

отв. x=0, x= -2, x=2

2. x(0.7x +8) =0
x=0
0.7x +8 =0
0.7x= -8
x= -8/0.7 (0.7=7/10)
x= -8 : 7/10
x= -8*10/7
x= -80/7
x= -11 3/7 (одиннадцать целых три седьмых)

отв. x=0, x= -11 3/7