Question

Решите систему уравнения 1) 2)

Answer 1

$x^2-y^2=-21\\ x+y=3\\ \\ (x-y)(x+y)=-21\\ x+y=-3\\ \\ x-y=7\\ x+y=-3\\ \\ x=7+y\\ 7+2y=-3\\ 2y=-10\\ y=-5\\ x=2$

$x^2+y^2=74 \\ x-y=2\\ \\ (x-y)^2+2xy=74\\ x-y=2\\ \\ 2xy=70\\ xy=35\\ \\ xy=35\\ x-y=2\\ \\ x=2+y\\ 2y+y^2=35\\ y^2+2y-35=0\\ D=12^2\\ y_{1}=\frac{-2+12}{2}=5\\ y_{2}=\frac{-2-12}{2}=-7\\ x=7\\ y=-5$