Question

{(x+y)(-2x+3y)=0
{4x-y=15

Answer 1

y=4x-15
(x+4x-15)(-2x+4x-15)=0
(5x-15)(2x-15)=0
10x^2-75x-30x+225=0
10x^2-105x+225=0
2x^2-21x+45=0
D=21^2-4*2*45
D=441-360
D=81
x1,2=-b+-кореньD/2a
x1,2=21+-9/4
x1,2=7.5;3
4x-y=15
30-y=15
y=15
12-y=15
y=-3