The length of one side of the triangle is 2 times the length of the second side, and the length of the third side is 1.5 cm

The length of one side of the triangle is 2 times the length of the second side, and the length of the third side is 1.5 cm less than the length of the first side. Find the lengths of the sides of a triangle if its perimeter is 12.5

Let the first side of the triangle be 2x, the second side x, and the third side 2x-1.5.
Let’s write down the abbreviated condition of the problem.
a – 2x;
b – x;
c – (2x-1.5);
P = 12.5 cm;
The formula for the perimeter of a triangle is: P = a + b + c;
We form an equation for the perimeter formula.
2x + x + (2x-1.5) = 12.5;
On the left side of the equation, we give similar terms, and transfer the known term to the right side, while changing its sign to the opposite.
5x = 12.5 + 1.5;
We give similar terms on the right side.
5x = 14;
To find an unknown factor, the product must be divided by a known factor.
x = 14: 5;
x = 2 4/5;
x = 2.8;
a = 2x = 2 * 2.8 = 5.6 (cm);
b = x = 2.8 (cm);
c = 2x-1.5 = 2 * 2.8-1.5 = 4.1 (cm).