Multiply Assume That Variables Used as Exponents Represent Positive Integers $$\left( \mathrm { x } ^ { \mathrm { a } } + 7 \right) \left( \mathrm { x } ^ { 2 \mathrm { a } } - 9 \right)$$

Multiple Choice

Multiply. Assume that variables used as exponents represent positive integers.
- $$\left( \mathrm { x } ^ { \mathrm { a } } + 7 \right) \left( \mathrm { x } ^ { 2 \mathrm { a } } - 9 \right)$$

A) $x ^ { 3 a } - 2 x ^ { a } - 63$
B) $x ^ { 2 a ^ { 2 } + 7 x ^ { 2 a } - 9 x ^ { a } - 63 }$
C) $x ^ { 3 a } - 2 x ^ { 2 a } - 63$
D) $x ^ { 3 a } + 7 x ^ { 2 a } - 9 x ^ { a } - 63$