In a rectangle, the side is 12 cm and the diagonal is 20 cm, find the perimeter.

univerkov | March 6, 2021 | education

Suppose we are given a rectangle ABCD with AB = 12 cm, AC = 20 cm.

Then we find its other side – BC – from the right-angled triangle ABC by the Pythagorean theorem.

BC = √ (AC ^ 2 – AB ^ 2) = √ (20 ^ 2 – 12 ^ 2) = √ (400 – 144) = √256 = 16 cm.

Find the perimeter of this rectangle using the formula P = 2 (a + b).

P = 2 (12 + 16) = 2 * 28 = 56 cm.

Answer: P = 56 cm.

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