Question

If the perimeter of the following triangle is 7x-2, what is the length of the unknown side?

Answer 1

unknown side = 7x-2 - (3x - 9 + x + 7)
unknown side = 7x - 2 -3x + 9 -x - 7
unknown side = = 3x

answer

unknown side = 3x

Answer 2

perimeter = s+s+s

so 7x-2 = (3x-9) + (x+7) + ?

3x-9 + x+7 = 4x-2

7x-2 - 4x-2 = 3x

remaining side is 3x