Find the perimeter of the triangle.

all the sides of the triangle are the same because this is equilateral. this means:

(21 - x) = (2x - 3) = (x + 5)

Let's take (x+5) and (2x - 3)

x + 5 = 2x - 3   subtract x from both sides

    5 = x -3   add 3 to both sides

          8 = x   you can rearrange this to x=8

Now it's the fun part! SUBSTITUTION! :D (sarcasm)

               BUT WAIT Remember, all of the sides are equal to one another! That means we only have to solve for one side!

Let's do the top side.     21 - 8 = 13

Since there are 3 sides in a triangle, we can easily multiply the 13 by 3

13 x 3 = 39     The perimeter is 39 inches

yes

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