Question

(14y+21)*(1,8-0,3y)=0

Answer 1

14y+21=0
14y=-21
y=-21:14
y=-1,5


1,8-0,3y=0
0,3y=1,8
y=1,8:0,3
y=6

ответ(-1,5;6)

Answer 2

(14y+21)(1.8-0.3y)=0
25.2y-4.2y²+37.8-6.3y=0
-4.2y²+18.9y+37.8=0 |*(-1)
4.2y²-18.9y-37.8=0
D=(-18.9)²-4*4.2*(-37.8)=357.21+635.04=992.25, √992.25=31.5
y₁=18.9+31.5/2*4.2=6
y₂=18.9-31.5/2*4.2=-1.5
Ответ: y₁=6, y₂=-1.5