How to determine if a triangle is right acute or obtuse based on side lengths?

To solve the system of equations below, pedro isolated the variable y in the first equation and then substituted it into the second equation. what was the resulting equation? { 5y=10x {x^2+y^2=36

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab

What is the perimeter of an equilateral triangle if each side is (x+3)?