Question

Which is a sum of cubes?

a3 + 18
a6 + 9
a9 + 16
a12 + 8

Answer 1

a^12+8

Explanation:

let's check all the expressions

1. a^3+18

here 18 is not a perfect cube.

2. a^6+9

here 9 is not a perfect cube.

3. a^9+16

here 16 is not a perfect cube.

4. a^16+8

here 8 is a perfect cube, thus we can write above expression by using laws of exponents as

(a^4)^3+2^3

Thus, is a sum of cubes.

a^12+8