1.(3a^2-5a+6)-3(-2a^2-2a+4)2.3a^2b-2[ab^2-2(a^2b-2ab^2)]3.3a^2-[7b-(4a-b)-2a^2]4.-7x^2+(6x^2-5xy)-2(3y^2+xy-x^2)^2是的平方 不要错误答案

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1.(3a^2-5a+6)-3(-2a^2-2a+4)2.3a^2b-2[ab^2-2(a^2b-2ab^2)]3.3a^2-[7b-(4a-b)-2a^2]4.-7x^2+(6x^2-5xy)-2(

1.(3a^2-5a+6)-3(-2a^2-2a+4)2.3a^2b-2[ab^2-2(a^2b-2ab^2)]3.3a^2-[7b-(4a-b)-2a^2]4.-7x^2+(6x^2-5xy)-2(3y^2+xy-x^2)^2是的平方 不要错误答案
1.(3a^2-5a+6)-3(-2a^2-2a+4)
2.3a^2b-2[ab^2-2(a^2b-2ab^2)]
3.3a^2-[7b-(4a-b)-2a^2]
4.-7x^2+(6x^2-5xy)-2(3y^2+xy-x^2)
^2是的平方 不要错误答案

1.(3a^2-5a+6)-3(-2a^2-2a+4)2.3a^2b-2[ab^2-2(a^2b-2ab^2)]3.3a^2-[7b-(4a-b)-2a^2]4.-7x^2+(6x^2-5xy)-2(3y^2+xy-x^2)^2是的平方 不要错误答案
1.(3a^2-5a+6)-3(-2a^2-2a+4)
=3a²-5a+6+6a²+6a-12
=9a²+a-6
2.3a^2b-2[ab^2-2(a^2b-2ab^2)]
=3a^2b-2ab^2+4(a^2b-2ab^2)
=3a^2b-2ab^2+4a^2b-8ab^2
=7a^2b-10ab^2
3.3a^2-[7b-(4a-b)-2a^2]
=3a^2-7b+4a-b+2a^2
=5a^2-8b+4a
4.-7x^2+(6x^2-5xy)-2(3y^2+xy-x^2)
=-7x^2+6x^2-5xy-6y^2-2xy+2x^2
=x^2-7xy-6y^2

an=1/(n+9/n)
n+9/n>=2√(n*90/n)=2√90
当n=90/n时取等号
即n=√90
则n最接近√90时最大
所以n=9或10
a9=1/19
a10=1/19
所以时第9和10项

1. (3a^2-5a+6)-3(-2a^2-2a+4)
=3a²-5a+6+6a²+6a-12
=9a²+a-6
2. 3a^2b-2[ab^2-2(a^2b-2ab^2)]
=3a^2b-2ab^2+4(a^2b-2ab^2)
=3a^2b-2ab^2+4a^2b-8ab^2
=7a^2b-10ab^2
3. 3a^2-[7b-(4a-b)-2a^2]
=3a^2-7b+4a-b+2a^2
=5a^2-8b+