Question

Given that x+y=4 and x^2-y^2=48.Find the value of 2x-2y

Answer 1

哈哈,又一道题.我再来一次.

先翻译一下这道题：

假如：x+y=4,x^2-y^2=48.试计算2x-2y.

答：

x^2 -y^2

= (x+y)*(x-y)

将x+y=4,x^2-y^2=48分别带入,

48 =4（x-y)

x-y =12

所以,

2x -2y = 2(x-y) =2*12 =24.