# Area Formulas

The standard notation for area is A.

#### Square

Let's a square side is long a then area formula is:

A = a.a = a2

#### Rectangle

Let's a rectangle sides are long a and b

A = a.b

#### Parallelogram

Let's palallelogram sides are long a and b and ha is the altitude to the side a, and hb is the altitude to the side b
Parallelogram area formula is:

A = a.ha = b.hb

Parallelogram area formula explained.(a java applet will be opened in a new window).

#### Trapezoid

Say the length of the parallel sides of a trapezoid are long a and b and the distance between the two bases is h(the trapezoid altitude). The area formula is:

A = ½(a + b)h

#### Area calculator

Enter the triangle:

#### Area of a right triangle

$S=\frac{a.b}{2}$

$S=\frac{c.h_c}{2}$

#### Triangle

ABC is a triangle

the length of the sides is: a, b, c and the length of the altitudes is: ha, hb and hc.

A = ½(a.ha) = ½(b.hb) = ½(c.hc)
A = ½(ab.sinC) = ½(ac.sinB) = ½(bc.sinA)
p = ½(a + b + c)
A = √p(p - a)(p - b)(p - c) - Heron's formula
A = R2sinA.sinB.sinC = abc/4R

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