When Rectangle has equal Height and Width then it is called as Square.

Formula for Rectangle Area is

Area = Width * Height

Therefore Area of Square formula can be written as

$\mathrm{Area}=a^2$
Where a is length of one side

When length of diagonal is given for square area of Square can be written as

$\mathrm{Area}=\frac{d^2}{2}$
Where d is length of diagonal

The area of a triangle is given by the formula below

$\mathrm{Area}=\frac{\mathrm{Base}\times \mathrm{Height}}{2}$

Therefore Triangle Formula can be written as

$a=\frac{b\times h}{2}$
Where
b is Base of Triangle
h is Height of Triangle

When length of two sides and angle between the two sides is given formula for area of triangle can be written as

$\mathrm{Area}=\frac{a\times b\times \mathrm{Sin\; C}}{2}$
Where
a and b is length of sides
C is angle between two sides a and b

The area of a Rectangle is given by the formula below

$\mathrm{Area}=\mathrm{Width}\times \mathrm{Height}$

Therefore Area of Rectangle formula can be written as

$\mathrm{Area}=w\times h$
Where
w is width of Rectangle
h is Height of Rectangle

The area of a Parallelogram is given by the formula below

$\mathrm{Area}=\mathrm{Base}\times \mathrm{Height}$

Therefore Parallelogram formula can be written as

$\mathrm{Area}=b\times h$
Where
b is base length of Parallelogram
h is Height of Parallelogram

Trapezoid has two parallel sides separated by distance called as height.

The area of a Trapezoid is given by the formula below

$\mathrm{Area}=\mathrm{Height}\times \frac{(\mathrm{base1}+\mathrm{base2})}{2}$

Therefore Area of Trapezoid can be written as

$\mathrm{Area}=h\times \frac{(a+b)}{2}$
Where
a and b are base lengths of Trapezoid
h is Height of Trapezoid

The area of a Circle is given by the formula below

$\mathrm{Area}=\mathrm{\pi }\times {\mathrm{Radius}}^2$

Therefore Circle area formula can be written as

$\mathrm{Area}=\mathrm{\pi }\times r^2$
Where
r is Radius of Circle
$\mathrm{\pi }=3.14$

If diameter is given Area of Circle can be written as

$\mathrm{Area}=\mathrm{\pi }\times \frac{d^2}{4}$
Where
d is diameter of Circle
$\mathrm{\pi }=3.14$

A circular sector or circle sector, is the portion of a disk enclosed by two radii and an arc. The area of a Sector is given by the formula below

When central angle of sector is given Area of Sector can be written as

$\mathrm{Area}=\frac{n}{360}\times \mathrm{\pi }{r}^2$
Where
r is Radius of Circle
n is Angle of sector
$\mathrm{\pi }=3.14$

When arc length of sector is given Area of Sector can be written as

$\mathrm{Area}=\frac{C}{2}\times r$
Where
r is Radius of Circle
C is Arc length of sector

The area of a Ellipse is given by the formula below

$a=\mathrm{\pi }\times \mathrm{a}\times \mathrm{b}$
Where
b is length of Long Axis
a is length of Short Axis
$\mathrm{\pi }=3.14$