Question

已知x+y=7,xy=10. 求(1)2(x²+y²)的值;(2)(x-y)^4

用分解因式做,谢谢!

Answer 1

解：
1）2(x²+y²)=2[(x+y)^2-2xy]=2*(49-20)=58
2)(x-y)^2=(x+y)^2-4xy=49-40=9
(x-y)^4=[(x-y)^2]^2=9^2=81

Answer 2

(1)2(x²+y²)的值
2(x²+y²)
=2(x+y)^2-4xy
=2*7^2-4*10
=98-40
=58

;(2)(x-y)^4
=[(x+y)^2-4xy]^2
=(7^2-4*10)^2
=(49-40)^2
=81