利用乘法公式计算(x+y)(x²+y²）（x-y)(x的四次方+y四次方)（a-2b+3)(a+2b-3)[(x-y)²+(x+y)²](x²-y²)(m-n-3)²先化简,再求值[(a-1/2)²-(a+1/2)²](a+3),其中a=-2
利用乘法公式计算
(x+y)(x²+y²）（x-y)(x的四次方+y四次方)
（a-2b+3)(a+2b-3)
[(x-y)²+(x+y)²](x²-y²)
(m-n-3)²
先化简,再求值
[(a-1/2)²-(a+1/2)²](a+3),其中a=-2
(x+y)(x²+y²）（x-y)(x的四次方+y四次方)
=(x+y)(x-y)(x^2+y^2)(x^4+y^4)
=(x^2-y^2)(x^2+y^2)(x^4+y^4)
=(x^4-y^4)(x^4+y^4)
=x^8-y^8
（a-2b+3)(a+2b-3)
=[a-(2b-3)][a+(2b-3)]
=a^2-(2b-3)^2
=a^2-4b^2+12b-9
[(x-y)²+(x+y)²](x²-y²)
=2(x^2+y^2)(x^2-y^2)
=2(x^4-y^4)
=2x^4-2y^4
(m-n-3)²
=m^2+n^2+9-2mn-6m+6n
[(a-1/2)²-(a+1/2)²](a+3)
=[(a-1/2)+(a+1/2)][(a-1/2)-(a+1/2)](a+3)
=2a(-1)(a+3)
=-2a^2-6a
将a=-2代入,得
[(a-1/2)²-(a+1/2)²](a+3)
=-2*（-2）^2-6*（-2）
=4
