因式分解 (1)25x2-81y2 (2)x3-2x2y+xy2 (3)x4-18x2+81.

问题描述:

因式分解
(1)25x2-81y2
(2)x3-2x2y+xy2  
(3)x4-18x2+81.

(1)25x2-81y2
=(5x+9y)(5x-9y);
(2)x3-2x2y+xy2  
=x(x2-2xy+y2
═x(x-y)2);
(3)x4-18x2+81
=(x2-9)2
=(x+3)2(x-3)2