Question

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

Answer 1

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