Question

find the length of the diagonal of a rectangle whose sides are 15 cm and 8cm

Answer 1

If we carefully consider the shape made by a diagonal and two sides of a rectangle then we find that it is a right angled triangle.

So,
In case of a right angled triangle we may apply the Pythagoras theorem.

The length of the triangle can be considered as the base of the triangle and the breadth can be considered the height adding to this that the diagonal is considered the hypotenuse.

So,
Perpendicular, p = 8 cm
Base, b = 15 cm
Hypotenuse, h = ?

By Pythagoras theorem,
h ^ 2 = p ^ 2 + b ^ 2
h ^ 2 = 8 ^ 2 + 15 ^ 2
h ^ 2 = 64 + 225
h ^ 2 = 289
h = √ 289
h = 17 cm

Hence,

Diagonal = Hypotenuse = h = 17 cm