Question

Помогите, пожалуйста, решить систему, срочно))) х-4у=3 и х^2 -21у=28

Answer 1

$left { {{x-4y=3} atop {x^2-21y=28}} right. \ x=3+4y \ (3+4y)^2-21y=28 \ 9+24y+16y^2-21y=28 \ 16y^2-3y-19=0\ D=9+4*16*19=1225 sqrt{D} =35\ y_{1} = frac{3+35}{2*16} =- frac{19}{16} \ \ y_{2} = frac{3-35}{2*16} = 1\\ x_{1}=3-4* frac{19}{16} =- frac{7}{4} \\ x_{2}=3+4=7$
(-7/4, -19/16)  (7, 1)

Answer 2

{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) }