已知多项式3x+my-8与多项式-nx+2y+7的差中不含x,y,则n的m次方+mn=__3_____
n+3=0;
n=-3;
m-2=0;
m=2;
己知a=-a-1,b=a+2a-3,则-a-3b结果为( -3a²-5a+19 )
a+1-3a²-6a+18=-3a²-5a+19;
若m+3mn=-3,则代数式5m-[5m-(2m-mn)-7mn-5]的值是__-1___
5m-5m+2m-mn+7mn+5
=2m+6mn+5
=2×(-3)+5
=-1;
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