x-4y=3
x^2-21y=28
x=3+4y
(3+4y)^2 - 21y=28
9+24y+16y^2-21y=28
16y^2-3y-19=0
d=9+1216=1225=35^2
y1=3+35/32=1целая 1/8
y2=3-35/32=-32/32=-1
y=-1
x=-1
y=1целая 1/8
x=7.75
