In a rectangle all of its angles are right angle triangle, since a diagonal divides the rectangle in two equal halves and it contains a right angle, the traingle formed is a right angle triangle.
We also know that in aright angle triangle (Base)2 + (Perpendicular)2 = (Hypotenues)2 =B2 + P2 = H2
So from the problem we get that the two sides of the rctangle are 16 cm 12 cm which are base perpendicular of the right angle triangle.
B2+ P2= H2
(16)2 + (12)2 = H2
H2 = 256 + 144
H2 = 400
H =√400
H = 20 cm.
So the diagonal of the rectangle = 20 cm.
Ans: 20 cm.