Answer: x = 39 because 39 + 102 = 141 and 180 - 141 = 39
Circumference of a circle - derivation
This page describes how to derive the formula for the circumference of a circle.
Recall that the definition of pi (π) is the circumference c of any circle divided by its diameter d. Put as an equation, pi is defined as
π
=
c
d
Rearranging this to solve for c we get
c
=
π
d
The diameter of a circle is twice its radius, so substituting 2r for d
c
=
2
π
r
If you know the area
Recall that the area of a circle is given by
area
=
π
r
2
Solving this for r
r
2
=
a
π
So
r
=
√
a
π
The circumference c of a circle is
c
=
2
π
r
Factoring out the 1/2 (that is the coefficient of the variable) would require you to divide the equation by one half, which is the same as multiplying by two. After doing this, the answer can be expressed as:
1/2 (d+12)
Area is equals length times (*) breath
L*b
10.3*9.3
=95.79l
