To find the length of the base, you must first find the length of the sides, or the value of x. Because it is an isosceles triangle, the legs are equal to each other.
2x + 4=x + 8
x=4
Now that you have found x, plug it into the equation for the base.
5(4) - 2
20 - 2
18
Final Answer: 18
Hope this helps!! :)
