凌宇之星
幼苗
共回答了21个问题采纳率:100% 举报
2X^2-Y+(2X^2-Y^2)-2(X^2+2Y^2)
=2X^2-Y+2X^2-Y^2-2X^2-4Y^2
=2X^2-Y-5Y^2
=2*1^2-2-5*2^2
=2-2-20
=-20
5(A+B^3)/7-3(2A+B+1/4)/14-11(4A+B)/21
=5A/7+5B^3/7-3A/7-3B/14-3/56-44A/21-11B/21
=-38A/21+5B^3/7-31B/42-3/56
=-38*(1/8)/21+5*(-1/2)^3/7-31*(-1/2)/42-3/56
=-19/84-5/56+31/84-3/56
=0
(5AB+7B+4A)-(4AB-3B)+(6A-3AB)
=5AB+7B+4A-4AB+3B+6A-3AB
=-2AB+10A+10B
=-2(AB)+10(A+B)
=-2*4+10*8
=72
1年前
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