Question

Which of the following expressions is equivalent to a9 - b9?

Answer 1

When you have the power multiplied to another power you have to multiply 
so 
(a^3)^3 - (b^3)^3 = a^9 - b^9

A is correct. 

B is incorrect because when you multiply the exponents you get a^18 - b^18 

C is incorrect because when you distribute the 2 you get a^6 - b^6 

D is correct too