Here's the formula to find area of a circle
[tex]\boxed{a= \pi \times r^{2}}[/tex]
And here's the formula to find circumference of a circle
[tex]\boxed{c=2 \times \pi \times r}[/tex]
Number 1
Find the area
a = π × r²
a = π × 4²
a = π × 16
a = 16π
The area of the first circle is 16π ft²
Find the circumference
c = 2 × π × r
c = 2 × π × 4
c = 8π
The circumference of the first circle is 8π ft
Number 2
The radius is not known yet. We have to find the radius from the diameter. Radius is half of the diameter.
r = [tex] \frac{1}{2} [/tex] × d
r = [tex] \frac{1}{2} [/tex] × 13
r = [tex] \frac{13}{2} [/tex]
Find the area
a = π × r²
a = π × [tex] ( \frac{13}{2}) ^{2}[/tex]
a = π × [tex] ( \frac{169}{4})[/tex]
a = [tex] \frac{169}{4} \pi[/tex]
The area of the second circle is [tex] \frac{169}{4} \pi[/tex] m²
Find the circumference
c = 2 × π × r
c = (2r) × π
remember radius is half of diameter, 2 radius equals a diameter
c = d × π
c =13 × π
c = 13π
The circumference is 13π m
