Решите системы уравнений) 1. xy=10 y^{2} — y^{2}=21

2x^2y-y=7 y (2x^2-1)=7 y (2x^2-1)=7xy-x+3y-3=0 x (y-1)+3 (y-1)=0 (x+3) (y-1)=0y=1 2x^2-1=7 x^2=4 (-2; 1) (2; 1) x=-32x^2-1=17y=7/17 (-3; 7/17) xy=10x^2-y^2=21 (x-y) (x+y)=7*3=(5-2) (5+2) x=5 y=2