Answer:
The third side is 10x-5
Step-by-step explanation:
The perimeter of a triangle is given by
P = s1+s2+s3 where s is the side of the triangle
23x-7 = 5x+7 + 8x-9 + s3
Combine like terms
23x-7 = 13x -2 +s3
Subtract 13x from each side
23x -13x-7 = 13x-13x -2 +s3
10x -7 = -2 +s3
Add 2 to each side
10x-7+2 = -2+2 +s3
10x -5 = s3
The third side is 10x-5
