Question

Two adjacent sides of a parallelogram are 21 cms and 20 cms. the diagonal joining the end points of these two sides is 29 cms. the area of the parallelogram (in sq.cms) is

Answer 1

A diagonal divides a parallelogram into 2 equal triangles

We first find the area of triangle formed by sides 21, 20 & diagonal of 29 cm

By herons formula:

S = A + B + C / 2

A = $\sqrt{S(S-A)(S-B)(S-C)}$ = 210 cm²

Area of parallelogram = 2 × Area of triangle = 2 × 210 = 420 cm²

Answer 2

A diagonal divides a parallelogram into 2 equal triangles

We first find the area of triangle formed by sides 21, 20 & diagonal of 29 cm

Now, we will find by herons formula:

S = a+b+c/2

Area =

$\sqrt{s(s - a)(s - b)(s - c)}$

= 210 cm²

Area of parallelogram = 2 × Area of triangle = 2 × 210 = 420 cm²

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