4(x-y)^2+7(x-y)=15
x-y=t;4t^2+7t-15=0
D=49+240=289=17^2
t1=(-7+17)/8=10/8=5/4
t2=(-7-17)/8=-24/8=-3
x-y=5/4;x-y=-3
2x+5y=1
1)x=y+5/4
2(y+5/4)+5y=1
2y+5/2+5y=1
7y=1-5/2
7y=-3/2;y=-3/2:7;y=-3/2•1/7=-3/14
x=y+5/4=-3/14+5/4=(-6+35)/28=29/28
2)x-y=-3;x=y-3
2(y-3)+5y=1;2y-6+5y=1
7y=7;y=1;x=y-3=1-3=-2
ответ {х=-2;у=1};{х=29/28;у=-3/14}