Find the missing side length, in terms of x

Question

A triangle has a perimeter of 23a^2--7a. Two of the side lengths are 6a+8a² and 8a²-9a. 

Answer 1

Perimeter is the sum of all the sides.  To find the missing side in this question, you would take the perimeter and subtract the two known sides:

 

23a²-7a - (6a+8a²)  - (8a²-9a) 

Distribute the minus signs to clear the parenthesis.

23a² - 7a - 6a - 8a² - 8a² + 9a

Collect like terms

23a² - 8a² - 8a²  - 7a - 6a + 9a

7a² - 4a

So the missing side is:  7a² - 4a