The length of the base of an isosceles triangle is x. The length of a leg is 3x−7. The perimeter of the triangle is 77. Find x.

x=13

Step 1: Define isosceles triangle

In an isosceles triangle, two sides and angles are equal. The equal sides will be the legs.

Step 2: Write an equation

To write an equation we must first consider the information discussed in step 1. Since we know that the legs will be equal, we will add that to the equation twice. The base and legs will be on one side of the equation, and the perimeter will be on the other. Now we can write the equation!

x+3x-7+3x-7=77

Step 3: Combine like terms

Like terms are terms that share the same variable, or lack of. Let’s add/subtract these now.

x+3x-7+3x-7=77
7x-14=77

Step 4: Solve for x

Let’s do the last part of the equation and solve for x, our final answer.

*Rewrite equation*
7x-14=77
*Add 14 to both sides*
7x=91
*Divide 7 on both sides*
x=13

This is your answer. Hope this helps! Comment below for more questions.