初一数学题：先化简，再求值 初一上册数学先化简再求值求15道先化简再求值题
\u6570\u5b66\u4e03\u5e74\u7ea7\u5148\u5316\u7b80\u518d\u6c42\u503c\u9898\u76ee\uff0c\u8d8a\u591a\u8d8a\u597d\u2026\uff08\u6709\u7b54\u6848\uff091.\u5148\u5316\u7b80\uff0c\u518d\u6c42\u503c\uff1a
[(a+b)(a\uff0db) \uff0d(a\uff0db)2+2b(a\uff0db)]\u00f74b,a=2,b=\uff0d2.
2.\u5df2\u77e5x+y=7,xy=2,\u6c42\u24602x2+2y2\u7684\u503c\uff1b\u2461(x\uff0dy)2\u7684\u503c.
1\u3001a\uff0db\uff0c4
2\u3001\uff081\uff0990
\uff082\uff0941
1\uff0e(3a2-4ab-5b2)-(2b2-5a2+2ab)-(-6ab)\uff0e
2\uff0exy-(2xy-3z)+(3xy-4z)\uff0e
3\uff0e(-3x3+2x2-5x+1)-(5-6x-x2+x3)\uff0e
4\uff0e3x-(2x-4y-6x)+3(-2z+2y)\uff0e
5\uff0e(-x2+4+3x4-x3)-(x2+2x-x4-5)\uff0e
6\uff0e\u82e5A=5a2-2ab+3b2,B=-2b2+3ab-a2,\u8ba1\u7b97A+B\uff0e
7\uff0e5m2n+(-2m2n)+2mn2-(+m2n)\uff0e
8\uff0e2(x2-2xy+y2-3)+(-x2+y2)-(x2+2xy+y2)\uff0e
9\uff0e2(a2-ab-b2)-3(4a-2b)+2(7a2-4ab+b2)\uff0e
10\uff0e\u6c42(3x2y-2xy2)-(xy2-2x2y),\u5176\u4e2dx=-1,y=2\uff0e
11\uff0e\u5df2\u77e5|x+1|+(y-2)2=0,\u6c42\u4ee3\u6570\u5f0f5(2x-y)-3(x-4y)\u7684\u503c\uff0e
12\uff0e\u5f53P=a2+2ab+b2,Q=a2-2ab-b2\u65f6,\u6c42P-[Q-2P-(P-Q)]\uff0e
13\uff0e\u6c422x2-\uff5b-3x+5+[4x2-(3x2-x-1)]\uff5d\u7684\u503c,\u5176\u4e2dx=-3\uff0e
14\uff0e\u5f53x=-2,y=-1,z=3\u65f6,\u6c425xyz-\uff5b2x2y-[3xyz-(4xy2-x2y)]\uff5d\u7684\u503c\uff0e
15\uff0e\u5df2\u77e5A=x3-5x2,B=x2-6x+3,\u6c42A-3(-2B)\uff0e
16\uff0e\u53bb\u62ec\u53f7\uff1a\uff5b-[-(a+b)]\uff5d-\uff5b-[-(a-b)]\uff5d\uff0e
17\uff0e\u53bb\u62ec\u53f7\uff1a-[-(-x)-y]-[+(-y)-(+x)]\uff0e
18\uff0e\u5408\u5e76\u540c\u7c7b\u9879\uff1a5m2n+5mn2-mn+3m2n-6mn2-8mn\uff0e
19\uff0e\u8ba1\u7b974x2-3[x+4(1-x)-x2]-2(4x2-1)\u7684\u503c\uff0e
20\u3001\u5df2\u77e5A=11x3+8x2-6x+2,B=7x3-x2+x+3,\u6c422(3A-2B)\uff0e
2、=-x^2-3x+2-x^2-4+4x=-2x^2+x-2=-50+5-2=-47
3、=3x^2y-2xy^2+2xy-3x^2y-xy+3xy^2=xy^2+xy=-12+6=-6
把括符打开，相同的加的加，减的减，乘的乘，最后算值哦，，，，
(1)原式=3b-1+5a^2-b-2a^2+4b=3a^2+6b-1 将a、b值带进去，=14
（2）原式=-x^2-3x+2-x^2-1/4+4x=-2x^2+x-1/4 =-181/4
(3)原式=3x^y-2xy^2+2xy-1.5x^2y+3xy^2=1.5x^y+xy^2+2xy =-18
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