myshiyu
幼苗
共回答了18个问题采纳率:100% 举报
①2xy-5yx-(-6x2次方y2次方)-3y2次方x2次方
=2xy-5xy+6x^2y^2-3x^2y^2
=3x^2y^2-3xy
=3xy(xy-1)
②(3a2次方-ab+1)-(-4a2次方+6ab+8)
=3a^2-ab+1+4a^2-6ab-8
=7a^2-7ab-7
=7(a^2-ab-1)
③已知A=3a2次方-2a+1,B=5a2次方-3a+2 求2A-3B
2A-3B
=2(3a^2-2a+1)-3(5a^2-3a+2)
=6a^2-4a+2-15a^2+9a-6
=-9a^2+5a-4
④若a-b+c=4/5 求25(b-a-c)
25(b-a-c)
=-25(-b+a+c)
=-25(a-b+c)
=-25*(4/5)
=-20
⑤先化简 求值
(4a2次方-2a-6)-2(2a2次方-2a-5)其中a=-1
=4a^2-2a-6-4a^2+4a+10
=2a+4
=2*(-1)+4
=-2+4
=2
-1/2a-2(a-1/2b2次方)-(3/2a-1/3b2次方)其中a=-2 b=2/3
=-1/(2a)-2a+1/b^2-3/(2a)+1/(3b^2)
=-2a-2/a+4/(3b^2)
=-2*(-2)-2/(-2)+4/[3*(2/3)^2]
=4+1+4
=9
1年前
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