七年级数学题 急！球方法过程
3x2-4x+7表示成a(x+1)2+b(x+1)+c的形式升御扒a(x+1)2+b(x+1)+c=a(x2+2x+1)+bx+b+c=ax2+(2a+b)x+(a+b+c)所以a=3 2a+b=-4 a+b+c=7解得a=3 b=-10 c=143x2-4x+7=3(x+1)2 - 10(x+1)+14(6x+7)2(3x+4)(x+1)-6=(36x2+84+49)(3x2+7x+4)-6设t=3x2+7x原式=(12t+49)(t+4)-6=12t2+97t+190=(4t+19)(3t+10) //因为12=3*4 190=19*10 97=3*19+4*10=(12x2+28x+19)(9x2+21x+10)=(12x2+28x+19)(3x+5)(3x+2) //因为9=3*3 10=2*5 21=3*5+3*2x2-x=7 y2-y=7相减x2-x-y2+y=0 (x+y)(x-y)=x-y 因为x-y≠0所以x+y=1 x2-x=7 y2-y=7 相加x2+y2-(x+y)=14 (x+y)2-2xy-(x+y)=14把x+y=1代入 (x+y)2-2xy-(x+y)=14 所以xy=-7x2+y2=(x+y)2-2xy=15原式=(x3+x2y)+(xy2+y3)=x2(x+y)+y2(x+y)=(x2+y2)(x+y)=15×1=15x^4-x2-2x-1 直接除以x2-x-1 x^4-x2-2x-1 =x2(x2-x-1) + x3 -2x-1=x2(x2-x-1) + x(x2-x-1) +x2 -x-1=(x2+x+1)(x2-x-1)所以这个多拆缺项式为x2+x+1[4x(2xy-3xy2)-3x2y（4-5y）]÷（-1/2xy）=[8x2y-12x2y2-12x2y+15x2y2]/（-1/2xy）=[-4x2y+3x2y2]/（-1/2xy）=-4x2y/（-1/2xy）+3x2y2/（-1/2xy）吵昌=8x-6xy
标签：七年级,数学题
