Answer: 8a-2
Step-by-step explanation:
The perimeter of a trapezoid is the addition of its four sides.
Perimeter of trapezoid= 39a – 7.
Length of 1st side= 9a,
Length of 2nd side= 5a + 1,
Length of third side= 17a – 6.
Length of the fourth side= Unknown
To find the length of the 4th side, we add the length of the three sides together and subtract from the perimeter of the trapezoid. This will be:
= 39a-7 - (9a+5a+1+17a-6)
= 39a-7-(9a+5a+17a+1-6)
= 39a-7-(31a-5)
=39a-7-31a+5
= 39a-31a-7+5
= 8a-2
The length of the 4th side is 8a-2
