Question

先化简,再求值：（a+2)(a-2)+2(a的平方+3),其中a=1/3.已知A=2x+y,B=2x-y,计算A的平方-

Answer 1

1.

(a+2)(a-2)+2(a²+3)

=a²-4+2a²+6 根据公式：(a+b)(a-b)=a²-b²

=3a²+2

带入a=1/3,得：

(a+2)(a-2)+2(a²+3)

=3a²+2

=3×（1/9）+2

=7/3

2.

A²-B²

=(A+B)(A-B)

=(2x+y+2x-y)(2x+y-2x+y)

=4x*2y

=8xy