x2+y2=y2-x2=(y+x)(y-x) 2-y2=(x+y)(xy)
练习： 1、判断下列各式能用平方差公式分解因式吗？ X2+y2 -x 2 -y 2 -x 2+y2 X2 -y 2 × × =y2 -x 2=(y+x)(y-x) =(x+y)(x-y)
仔细填一填 (1)9y2=(3y (2)0x2=19、P 25 9 C∠
仔细填一填 ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 2 2 2 4 9 3 25 36 2 1 9 = = = t x y x 5 6 3yt 2 3