**The adjacent sides of a parallelogram are 21 cm and 28 cm. If its one diagonal is 35 cm; find the area of the parallelogram.**

###### Answers:

First we find area of ABC.

Sides are, a = 28 cm

b = 35 cm

and c = 21 cm

S = (a + b + c)/2

= (28 + 35 + 21)/2

= 84/2 = 42 cm

**= 2 × 21 × 7**

**= 294 cm ^{2}**

**∵ Diagonal of ∥ gm divides it into two equal parts.**

**∴ area of ∥ gm = 2 × area of ∆ ABC**

**= 2 × 294**

**= 588 cm ^{2}**