# The Area of a Parallelogram

A parallelogram is a quadrilateral whose opposite sides are of equal length and parallel. The diagonals of a parallelogram are unequal and bisect each other. If $$ABCD$$ is a parallelogram, then its area can be calculated in two ways.

**(a) When the base and height are given:**

Since $$ABCD$$ is a parallelogram with base $$AB = b$$ and height, $$h = DL$$

$$\therefore $$ the area of the parallelogram $$ABCD$$ $$ = $$ the area of the rectangle $$DLMC$$.

The area of the parallelogram $$ = LM \times DL$$.

The area of the parallelogram $$ = AB \times h$$ (as $$LM = AB$$).

The area of the parallelogram $$ = b \times h$$.

$$\therefore $$ the area of the parallelogram $$ = $$ base $$ \times $$ height.

**(b) When the adjacent sides and their included angle is given:**

Since $$ABCD$$ is a parallelogram, take $$AB$$ and $$CD$$ as its two adjacent sides with the included angle $$\theta $$.

$$\therefore $$ the area of the parallelogram $$ = AB \times DL = b \times h$$

But $$\frac{h}{{AD}} = \sin \theta $$

Or $$h = AD\sin \theta $$

Or $$h = c\sin \theta $$.

$$\therefore $$ the area of $$ABCD = h \times c\sin \theta $$

$$\therefore $$ the area of the parallelogram $$ = $$ the product of the adjacent sides$$ \times \sin \theta $$

__Example__:

Find the base of a parallelogram whose area is $$256$$ square cm and height $$32$$ cm.

__Solution__:

Since the area $$ = 256$$ square cm

The height $$ = 32$$ cm

$$\therefore $$ the area of the parallelogram $$ = $$ base $$ \times $$ height.

$$\therefore $$ $$256 = $$base $$ \times 32$$.

The base $$ = \frac{{256}}{{32}} = 8$$ cm.

__Example__:

Find the area of a parallelogram, two adjacent sides of which are $$17$$ cm and $$20$$ cm and their included angle is$${60^ \circ }$$.

__Solution__:

Here, one side $$b = 17$$cm, the other side $$c = 20$$cm, and $$\theta = {60^ \circ }$$

$$\therefore $$ the area $$ = bc\sin \theta $$

$$ = 17 \times 20 \times \sin {60^ \circ }$$

$$ = 340 \times 0.866$$

$$ = 294.44$$ square cm.

David

November 27@ 4:33 amIn this tutorial there are a few errors: In situation (b) when the adjacent sides and their included angle are given, the correct adjacent sides to angle θ are AB and AD, not AB and CD as stated.

Also in same the correct formula for the area of ABCD is b × c sin θ, not h × c sin θ, since area = b x h and h = c sin θ.