八年级上册数学整式的乘法因式分解

(1) (X-1)^2≥0 X^2-2X+1≥0 X^2+1≥2X(2) a+b=1 (a+b)^3=1 即 a^3+3a^2b+3ab^2+b^3=1a^3+3ab(a+b)+b^3=1a^3+3ab+b^3=1(3) x²+y²+z²=xy+yz+xz x²+y²+z²-xy-yz-xz=02( x²+y²+z²-xy-yz-xz)=0x²+y²-2xy+ x²+z²-2xz+y²+z²-2xz=0(x-y)²+(y-z)²+(x-z)²=0因为 (x-y)²≥0,(y-z)≥0,(x-z)²≥0当且仅当 x=y y=z x=z 时,上述各项均等于0所以有:x=y=z