An equilateral triangle has a perimeter of 21 and a side length of 2x - 3. Solve for x

Answer:
In any triangle, Perimeter (P) = a + b + c, where, a, b and c are the sides and P is the perimeter of the triangle
In case of equilateral triangle, the length of all sides are equal. Therefore,
P = a + a + a = 3a
Here, a = (2x - 3) and P = 21
or, 21 = 3 (2x - 3)
or, 7 = 2x - 3
or, 2x = 10
or, x = 5