Question

求数学题的解答方法和步骤？

已知xy=7 (x-2)(y+2)=15 求x²+3xy+y²等于多少

Answer 1

根据题意

xy-2y+2x-4=15

7-2y+2x-4=15

2x-2y=12

x-y=6

两边平方

x²-2xy+y²=36

x²-2xy+y²+5xy=36+5xy

x²+3xy+y²=36+5X7=71

Answer 2

(x-2)(y+2)=15
xy+2x-2y-4=15
7+2x-2y-4=15
2x-2y=12
x-y=6
(x-y)^2 =36
x^2-2xy +y^2 =36
x^2+3xy +y^2 =36 +5xy
x^2+3xy +y^2 =36 +35 =71