The sum of the lengths of the sides of the rectangle is 42 cm, the length is 12 cm, what is the width of the rectangle?

Given:

P = 42 cm,

b = 12 cm.

Find – a.

Solution

By defining the perimeter of a rectangle:

P = 2a + 2b.

From the perimeter formula, we derive the formula for finding the width of the rectangle:

2a = P – 2b;

a = (P – 2b) / 2.

Let’s substitute the numerical values into the derived formula:

a = (42 – 2 * 12) / 2 = (42 – 24) / 2 = 18/2 = 9 (cm).

Answer: 9 cm.

Examination:

P = 2 * 9 + 2 * 12 = 18 + 24 = 42 (cm).