The perimeter of a triangle is 78 cm. One side is 15 cm. The other is 2 times larger. What is the third side of the triangle?

As you know, the perimeter of a triangle is the sum of all sides, and is calculated using the following formula: P = a + b + c.
From the condition of the problem, we know: the perimeter P = 78 cm, one side a = 15 cm, the other side is twice as large as the first, which means b = a * 2 = 15 * 2 = 30 cm.
Substitute all the known values of the sides and perimeter of the triangle into the formula and find the third side: 78 = 15 + 30 + s.
78 = 45 + s.
c = 78 – 45 = 33 cm.
Answer: The length of the third side of the triangle is 33 cm.