In order for the triangle to be isosceles, we have to set two lengths of the triangle equal to each other.
Let's take the lengths 5x-12 and x+20 and set them equal to each other.
5x - 12 = x + 20
Combine like terms by moving them over to their respective sides.
Subtract x from both sides of the equation.
4x - 12 = 20
Add 12 to both sides of the equation.
4x = 32
Divide both sides by 4.
x = 8
Check your answer by substituting.
5x - 12 = x + 20
5(8) - 12 = 8 + 20
40 - 12 = 28
28 = 28
Solution: x = 8