The area is associated with the number of square units contained in it.
Triangles
Recall the figure of parallelogram, that the diagonal of a parallelogram divides it into two congruent triangles
Therefore the area of one triangle is half the area of the parallelogram.
Recall that the area of a parallelogram is A = ba, so for a triangle,
A = 1/2 ba
Also,
b = 2A ÷ a
and
a = 2A ÷ b
where :
A = area
b = base
a = altitude
Rectangles
The area of a rectangle is the product of its length and its width. That is,
A = area
l = length
w = width
A = lw
l = A ÷ w
w = A ÷ l
Squares
A square is a special rectangle wherein the length and the width are equal, its area is the square of a side, that is,
A = s • s or A = s^2
Also, s = √A read as "the side is equal to the square root of the area"
Parallelogram
The area of a parallelogram is equal to the product of its base and its altitude. The altitude is the perpendicular distance from the base to the top.
Let A = area
b = base
a = altitude or height
then,
A = ba
Also,
b = A ÷ a
and
a = A ÷ b
Trapezoid
The area of trapezoid is half the product of the altitudes and of the sum of the bases. In symbols,
If we let b1 = the shorter base
b2 = the longer base
then,
A = 1/2 a ( b1 + b2 )
Circle
The area of a circle is π times the radius squared. In terms of diameter of the circle,
A = (πd^2) / 4
Since
r = ( 1/2 )d
Where
A = area
d = diameter
r = radius
π ~ 3.1416 ~ 22/7
Also,
r = √A÷π
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