A triangle has a perimeter of 7x-2y+15 and has sides of length 5x+y and 7+x, what is the length of the third side?

x - 3y + 8

Step-by-step explanation:

The perimeter of a triangle is sum of all the three sides.

One side is 5x + y

Another side is 7 + x

Let third side be m

And perimeter is 7x - 2y + 15

We simply sum the 3 sides and equate it to expression of perimeter and find m (third side). Shown below:

5x + y + 7 + x + m = 7x - 2y + 15

6x + y + 7 + m = 7x - 2y + 15

m = 7x - 2y + 15 - 6x - y - 7

m = x - 3y + 8

This is the length of the third side "x - 3y + 8"