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十字相乘法因式分解

一丶教学目标:. 十字相乘法因式分解. 二丶复习提问; 1:计算: (1). ( x+2)(x+3); (2). (x+2)(x-3); (3). (x-2)(x-3); (4)(x+a)(x+b);. 反过来:. ( x+a)(a+b). 三丶试一试:. a 与 b 和是一次项的系数. x x. 6 -3. 解:原式=. ( x + 6). ( x -3 ). (1). 因式分解 竖直写;. (2). 交叉相乘 验中项;

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十字相乘法因式分解

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  1. 一丶教学目标: 十字相乘法因式分解 二丶复习提问; 1:计算: (1). (x+2)(x+3); (2). (x+2)(x-3); (3). (x-2)(x-3); (4)(x+a)(x+b);

  2. 反过来: (x+a)(a+b) 三丶试一试: a与b和是一次项的系数 x x 6 -3 解:原式= (x+6) (x-3) (1).因式分解竖直写; (2).交叉相乘验中项; 6x-3x=3x (3).横向写出两因式; (x+6)和(x-3)

  3. x x 3 -5 (x+3) (x-5) -5x+3x=-2x 例2把 a a 5 2 解:原式= (a+5) (a+2) 2a+5a=7a ab ab -2 -5 (ab-5) (ab-2) 解:原式= -5ab-2ab=-7ab m m -5 4 解:原式= =3m (m-5) (m+4) 4m-5m=-m

  4. 结果为 A 练习一选择题: 结果为 A C 结果为 D

  5. 本课学习用十字相乘法把某二次项系数是__的二次三项式x+px+q 分解因式,如果q=ab,并且p=____,那么这个二次三项式可以分解因式. 因此,解题前先把常数项q分解因数(a和b),再看其和是否等于_______ ______ 1 a+b 小结: 一次项 系数p.

  6. 练习二丶把下列各式分解因式: 解:原式=(x+3)(x+1) 解:原式=(y-3)(y-4) 解:原式=(p-9)(p+4) 解:原式=(m+9)(m-2) =3(t-4)(t+2) =y(x-1)(x+2)

  7. x x 4 -7 提高题1把下列各式分解因式 4x-7x=-3x (x+4) (x-7) x x -y -2y =xy (x-2y) (x-y) -2xy-xy=-3xy x x 1 -7 -7x+x=-6x (x+1) (x-7)

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