1.已知2^m=3,2^n=5,则2^3m-2n=?2.（2/3 a^4b^7-1/9 a^2b^6) / (- 1/3
2个回答
1.已知2^m=3,
2^n=5,
2^3m-2n=2^3m/2^2n=(2^m)^3/(2^n)^2=3^3/5^2=27/25
2.（2/3 a^4b^7-1/9 a^2b^6) / (- 1/3 ab^3)^2
=2/3 a^4b^7 / (- 1/3 ab^3)^2-1/9 a^2b^6 / (- 1/3 ab^3)^2
=2/3 a^4b^7 /(1/9 a^2b^6)-1/9 a^2b^6 /(1/9 a^2b^6)
=6a^2b-1
3.简便计算
（3x^m）^2*(- 4/3 x)^2+(2x^m+1)^2
=（9x^2m）*(16/9 x^2)+4x^(2m+2)
=16x(2m+2)+4x(2m+2)
=20*x(2m+2)
4.[（xy+2）(xy-2)-2(x^2 y^2-2)] / (xy),
=(x^2y^2-4-2x^2y^2+4)/(xy)
=-x^2y^2/(xy)
=-xy
=10*(- 1/25)
=-2/5
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