用双十字相乘法分解因式:  (1)x2-8xy+15y2+2x-4y-3;   (2)x2-xy+2x+y-3;

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用双十字相乘法分解因式:  (1)x2-8xy+15y2+2x-4y-3;   (2)x2-xy+2x+y-3;
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用双十字相乘法分解因式:  (1)x2-8xy+15y2+2x-4y-3;   (2)x2-xy+2x+y-3;
用双十字相乘法分解因式:  (1)x2-8xy+15y2+2x-4y-3;   (2)x2-xy+2x+y-3;

用双十字相乘法分解因式:  (1)x2-8xy+15y2+2x-4y-3;   (2)x2-xy+2x+y-3;
x2-8xy+15y2+2x-4y-3;
=(x-3y)(x-5y)+2x-4y-3
x-3y -1
x-5y 3
x2-8xy+15y2+2x-4y-3=(x-3y-1)(x-5y+3)
(2)x2-xy+2x+y-3
=(x+2y)(x-y)+2x+y-3
x+2y 3
x-y -1
x2-xy+2x+y-3=(x+2y+3)(x-y-1)

分解形如ax^2+bxy+cy^2+dx+ey+f 的二次六项式 在草稿纸上,将a分解成mn乘积作为一列,c分解成pq乘积作为第二列,f分解成jk乘积作为第三列,如果mq+np=b,pk+qj=e,mk+nj=d,即第1,2列和第2,3列都满足十字相乘规则。则原式=(mx+py+j)(nx+qy+k)
15=3*5,-8=-3+-5,
-3=-1*3,2=-1+3;-4=-3*3...

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分解形如ax^2+bxy+cy^2+dx+ey+f 的二次六项式 在草稿纸上,将a分解成mn乘积作为一列,c分解成pq乘积作为第二列,f分解成jk乘积作为第三列,如果mq+np=b,pk+qj=e,mk+nj=d,即第1,2列和第2,3列都满足十字相乘规则。则原式=(mx+py+j)(nx+qy+k)
15=3*5,-8=-3+-5,
-3=-1*3,2=-1+3;-4=-3*3+5
(1)x2-8xy+15y2+2x-4y-3=(x-3y-1)(x-5y+3)
(2)x2-xy+2x+y-3=(x-y+3)(x-1)

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x2-8xy+15y2+2x-4y-3=x2-(8y-2)x+15y2-4y-3=x2-(8y-2)x+15y2-4y-3=x2-(8y-2)x+(3y+1)(3y-3)
=(x-3y-1)(x-5y+3)
x2-xy+2x+y-3=x2-(y-2)x+y-3=【x-(y-3)】【x-1】