Question

计算下列几道题★

1.（2x+y-5z)(2x+y+5z)
2.16(y+3)^2(y-3)^2-(2y+1)^2(2y-1)^2
3.(1/2x-1/3y)(1/2x+1/3y)(1/4x^2+1/9y^2)

Answer 1

解：
1.（2x+y-5z)(2x+y+5z)=(2x+y)^2-(5z)^2=4x^2+y^2+4xy-25z^2

2.16(y+3)^2(y-3)^2-(2y+1)^2(2y-1)^2=[4(y^2-9)]^2-(4y^2-1)^2
=(4y^2-36)^2-(4y^2-1)^2=(4y^2-36+4y^2-1)(4y^2-36-4y^2+1)
=(8y^2-37)(-35)=1295-280y^2

3.(1/2x-1/3y)(1/2x+1/3y)(1/4x^2+1/9y^2)
=(1/4x^2-1/9y^2)(1/4x^2+1/9y^2)
=1/16x^4-1/81y^4

主要是应用平方差公式
希望可以帮到你