[求助]GWD29-24

ilovecushi

Q24:

Which of the following is closest in value to 9⁹ – 9² ?

 

A.    9⁹

B.     9⁸

C.     9⁷

D.    9⁶

E.     9⁵

答桊是A

 想请教思路~~

gchen030

=9^2(9^7-1)

=9^2*9^7

=9^9