The perimeter of the triangle is 186 mm, the length of one side is 42 mm, the second side

The perimeter of the triangle is 186 mm, the length of one side is 42 mm, the second side is twice as large from it, which is equal to the 3 side of the triangle.

Let’s analyze the condition of the problem. To solve the problem, we use the formula for the perimeter of a triangle. The solution to the task of actions with explanations is presented below:

1. Let’s calculate what the second side of the triangle is equal to: 42 × 2 = 84 mm.

2. The perimeter of a triangle is equal to the sum of the lengths of all sides of this triangle, therefore the third side of the triangle is equal to the difference between the perimeter of this figure and two known sides, namely c = P – a – b. To calculate the length of the third side, you need to substitute numerical data in the derived formula: c = 186 – 42 – 84 = 60 mm.

Answer: 60 mm.