例1 计算：
(1) ( 3x + 1 )( x – 2 ) ;3x2 – 5x - 2
(2) ( x – 8 y )( x – y ) .x 2 - 9xy + 8y2
(1) (2x+1)(x+3); (2) (m+2n)(m+ 3n):
(3) ( a - 1)2 ； (4) (a+3b)(a –3b ).
(5) (x+2)(x+3); (6) (x-4)(x+1)
(7) (y+4)(y-2); (8) (y-5)(y-3)
答案: (1) 2x2+7x+3; (2) m2+5mn+6n2;
(3) a2-2a+1; (4) a2-9b2
(5) x2+5x+6; (6) x2-3x-4;
(7) y2+2y-8; (8) y2-8y+15
确定下列各式中m的值:
(1) (x+4)(x+9) = x2 + m x + 36
(2) (x-2)(x-18) = x + m x + 36
(3) (x+3)(x+p) = x + m x + 36
(4) (x-6) (x-p) = x + m x + 36
(5) (x+p)(x+q) = x + m x + 36
(p,q为正整数)
(1) m =13
(2) m = - 20
(3) p =12, m= 15
(4) p= 6, m= -12
(5) p = 4,q = 9, m =13
p=2,q = 18, m=20
p = 3, q =12, m=15
p=6, q= 6, m=12
p=1, q= 36, m=37
解方程与不等式:
(1) (x-3)(x-2)+18 = (x+9)(x+1);
(2) (3x+4)(3x-4) ＜9(x-2)(x+3).