1、一、计算:一、计算:)9)(5(xx(1)(2)(3)6)(23(xx(4)18)(4(xx45142xx138292xx72142xx()()xa xb)5)(12(xx6072xx2()xa b x ab)9)(5(xx)6)(23(xx)18)(4(xx45142xx138292xx72142xx)5)(12(xx6072xx762xx)1)(7(xxxx7171步骤:步骤:xxx67 1582xx)3)(5(xxxx35xxx8)5()3(qpxx2bapabq,2256712xxxx226310 xxxxqpxx2bapabq,)9)(5(xx)6)(23(xx)18)(4(xx)5
2、)(12(xx6072xx45142xx72142xx138292xx_342 xx_322 xx2092 yy_56102tt_-1、2、五、选择题:五、选择题:以下多项式中分解因式为以下多项式中分解因式为 的多项式是的多项式是()46xx A 2422xx2422 xxB2422xx2422 xxCD46xxc1662xx1662xx28xx1662xx 121315222xxxx301718322xyxy42132aa将下列多项式因式分解将下列多项式因式分解(1)x2+3x-4 (2)x2-3x-43(3)x2+6xy-16y2 (4)x2-11xy+24y2(5)x2y2-7xy-18
3、 (6)x4+13x2+36(2x+3)(x+4)=2x2+11x+122x1x342x4+1x3=11x结果中一次项系数是分解后十字交叉相乘所得的和(2x+3)(x-4)=2x2-5x+122x1x3-42x(-4)+1x3=-5x结果中一次项系数是分解后十字交叉相乘所得的和 例例1、用十字相乘法分解因式、用十字相乘法分解因式 2x2-2x-122x2-2x-12x2x-34x4+2x(-3)=-2x=(x-3)(2x+4)=2(x-3)(x+2)法一:法一:例例1、用十字相乘法分解因式、用十字相乘法分解因式 2x2-2x-122x2-2x-12x2x2-6x(-6)+2x2=-2x=(x+2)(2x-6)=2(x+2)(x-3)法二:法二:1529122xx)34)(53(xx:原式所以xx4335xxx29)20()9(22752yxyx)(72(yxyx:原式所以x2xy7y1xyxyxy572 9922baba322)3(32)3(babababababa233bababa963(1)2x2+13x+15(2)3x2 15x 18 (3)6x2-3x 18 (4)8x2-14xy+6y2(1)4x2+11x+6(2)3x2+10 x+8 (3)6x2-7xy 5y2 (4)4x2-18x+18 (5)4(a+b)2+4(a+b)-15