Решить систему, х-4у=3 и х^2 -21у=28

{x-4y =3 ; x² -21y =28 .
{x=4y +3 ; (4y+3)² -21y =28 .
(4y+3)² -21y =28 .
16y² +3y -19 =0 ;
D =3² -4*16*(-19) =9 +64*19 =9+1216=1225=35²⇒√D =35.
y₁=(-3 -35)/(2*16) = -19/16⇒x₁ =4(-19/16)+3 = -19/4+3 = -7/4.
y₂ =(-3+35)/(2*16) =32/32 =1⇒x₂ =4*1+3 =7.
ответ: {(-7/4 ; -19/4) , (7;1) }

(-7/4, -19/16)  (7, 1)