Answer:
a² + a - 72
Explanation:
An easy way of multiplying two equations in parentheses is FOIL:
First
Outer
Inner
Last
In order, you multiply:
The first values in the parentheses (first and third, in order from left to right), which are:
a and a, so it can be written as: a²
The outer values in the parentheses (first and fourth), which are:
a and -8, so it is -8a
The inner values (second and third), which are:
9 and a, so it would be 9a
The last values (second and fourth), which are:
9 and -8, which is -72
Writing them all together gives us a quadratic equation:
a² + 9a - 8a - 72
Combining the like terms gives us the final answer:
a² + a - 72