we know that
In an isosceles triangle, the two equal sides are called legs, and the remaining side is called the base
so
In this problem
Let
x---------> the length side of the legs
y---------> the length side of the base
Perimeter of the triangle is equal to

substitute the values and solve for x

therefore
the answer is
The equation that can be used to find the value of x is

The value of x is
