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
First, since we must follow PEMDAS, we need to do the operation that is first, which is addition.
-3.9 + 6.01 ← Adding a negative means subtracting, then giving the sign of the bigger number.
So now we solved those and we got this answer: 2.11
Now, we need to subtract and re-write the expression.
2.11 - (-7.423) = 2.11 + 7.423= 9.533
Ok....so now we have our final answer, and we have the choices above.
The only answer that matches ours is the last one.
Final answer: 9.533
Hope I helped ^_^
To solve an equation with a rational (fraction) coefficient you need to multiply both sides of the equation by the reciprocal (invert the fraction - flip it).
The reciprocal of 1/6 is 6/1 or 6
The product of reciprocals equals 1
1x = 24
x = 24
