(x+y+z)(x-y-z)
=[x+(y+z)][x-(y+z)] (平方差公式)
=x²-(y+z)²
=x²-y²-2yz-z²
(x+y+z)(x-y-z)
=(x+y+z)[x-(y+z)]
=x^2-(y+z)^2
=x^2-y^2-z^2-2yz
4yz =[(-y-z) x][(-y-z)-x]-[(-y z)-x][(-y z) x] 套公式得 =4yz 等于4YZ
(x+y+z)(x-y-z)=x²-(y+z)²=x²-y²-z²-2yz
(x+y+z)(x-y-z)
=(x+(y+z))(x-(y+z))
=x²-(y+z)²
=x²-(y²+2yz+z²)
=x²-y²-z²-2yz