Question

若x-2y=15,xy=-25,求x^2+4y^2-1的值是多少?

Answer 1

x=15+2y,代入xy=-25,(2y+5）*（y+5）=0,y=-5/2,x=10;y=-5,x=5 x^2+4y^2-1=10^2+4(-5/2)^2-1=124 x^2+4y^2-1=5^2+4(-5)^2-1=124