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(x+3y)(x-2y)-x3÷x+6y2,其中x=2,y=-3

计算题:(1)99×101 (公式法)(2)(4x2y+5xy-7y)-(5x2y-4xy+x)(3)(x-2y)2+4(x-y)(x+y);

(1)原式=(100-1)(100+1),
=1002-1,
=10000-1,
=9999;

(2)(4x2y+5xy-7y)-(5x2y-4xy+x),
=4x2y+5xy-7y-5x2y+4xy-x,
=(4-5)x2y+(5+4)xy-7y-x,
=-x2y+9xy-7y-x;

(3)(x-2y)2+4(x-y)(x+y),
=x2-4xy+4y2+4x2-4y2
=5x2-4xy;

(4)设:a+2b=m,
则原式(a+2b-c)(a+2b+c)=(m-c)(m+c),
=m2-c2
∵a+2b=m,
∴m2-c2=(a+2b)2-c2
=a2+4ab+4b2-c2

(5)(2x3y4z2+4x3y3z3-6x2y3z5)÷(2x2yz2),
=2x3y4z2÷2x2yz2+4x3y3z3÷2x2yz2-6x2y3z5÷2x2yz2
=xy3+2xy2z-3y2z3

(6)(x+3y)(x-2y)-x3÷x+6y2
=x2+xy-6y2-x2+6y2
=xy,
当x=2,y=-3时,
原式=2×(-3)=-6

先化简,再求值:(x-3y)(2x+y)-(x-2y)(x-3y),其中x=2,y=

解:原式= (x-3y) (2x+y-x+2y)
= (x-3y) (x+3y) =x 2 -9y 2
当x=2,y= 时,原式=4-9× =0

-x^2+2xy/6y^2-3xy其中x=2,y=3先化简,再求值

原式=[x(-x+2y)]/[3y(-x+2y)] =x/(3y) 把x,y的值代入,即=2/9

先化简,再求值:-xˇ2+2xy/6yˇ2-3yx,其中x=2,y=3.

-xˇ2+2xy/6yˇ2-3yx, =-x(x-2y)/[-3y(x-2y)] =x/3y 其中x=2,y=3. 上式=2/(3*3) =2、9

2道数学题目!~~

第一个,分解因式(x+3y)*(x+2y)=0 所以,两种情况,x=-3y或x=-2y,所以答案-3,-2 第二个无实根
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