1.若m-n=4,mn=1,求（9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值

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1.若m-n=4,mn=1,求（9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值
2.已知代数式2a的平方+3a+1的值为6,求代数式6a的平方+9a+5的值
3.长为（2a+3b）,宽为（a+b）的长方形,长减去（a-b）,宽减去1/2（a－b）后,其周长为多少?

1.9-2mn+2m+3n-3mn-2n+2m-m-4n-mn=9-6mn+3m-3n=9-6mn+3(m-n)=9-6+12
=15
2.因为:2a^2+3a+1=6,即:2a^2+3a=5,
所以:原式=3(2a^2+3a)+5=3*5+5=15+5=20.
3.周长=2(2a+3b)+2(a+b)-2(a-b)-(a-b)=4a+6b+2a+2b-2a+2b-a+b
=3a+11

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