Question

find the length of a diagonal of a rectangle whose sides are 21 cm and 20 cm

Answer 1

$\huge\red{Answer\: is}$

Length = 21 cm
Breadth = 20 cm

Now the diagonal of rectangle is
$= \sqrt{(21) {}^{2} + (20) {}^{2} } \\ = \sqrt{441 + 400} \\ = \sqrt{841} \\ = 29 \: cm$
Hope it helps you

Answer 2

Let ABCD be the rectangle.

AB=20cm. BC=21cm.

Let AC be the diagonal.

In Triangle ABC,

/_ABC=90.(angle of rectangle).

By Pythagoras theorem,

(AC)2=(AB)2+(BC)2

=(20)2+(21)2

=400+441

=841

=√841

29