Respuesta :

Answer : Third side will be x-3y+8 .

Explanation :

We have given that,

Length of  first side of triangle = 5x+y

Length of  second side of triangle = 7+x

Perimeter of triangle = 7x-2y+15

Now , we know that " Perimeter means sum of boundary",

So,

[tex]Perimeter = 5x+y+7+x+\text{ third side}\\7x-2y+15=5x+y+7+x+\text{third side}\\7x-2y+15-5x-y-7-x=\text{third side}\\x-3y+8 = \text{third side}[/tex]

So, Length of third side will be x-3y+8.