Question

若x+y=负1,xy=负5,求2x的平方+2y的平方的值

Answer 1

2x^2+2y^2=2(x^2+y^2)=2[(x+y)^2-2xy]

=2[1+10]

=22

2)

x^2-4y^2=6

x+2y=3①

x^2-4y^2=(x+2y)(x-2y)=6

=> x-2y=2②

联立方程①②

解得x=5/2

y=1/4