Find the perimeter of the rectangle whose length is 40 cm and a diagonal is 41 cm.

In a rectangle, all interior angles are of 90º measure. Therefore, Pythagoras theorem can be applied here.

(41)² = (40)² + x²

1681 = 1600 + x²

x² = 1681 − 1600 = 81

x = 9 cm

Perimeter = 2(Length + Breadth)

= 2(x + 40)

= 2 (9 + 40)

= 98 cm