mario’s is the better value
Use the circle area formula to work out the area of the pizza in each
deal. Is MegaSlice really a better value?
Area = ∏r
Mario’s 18” pizza: radius = 18 = 9 inches
∏ x 9
= ∏ x 81 = 254.5 sq inches
MegaSlice 12” pizza: radius = 12 = 6 inches
Area = 2 x
∏ x 6
= 2 x ∏ x 36 = 226.2 sq inches
io’s is MOR
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Eek—2πr and πr
look pretty similar don’t you think? Is
there a way to keep them straight so I don’t mix them up?
A:There are a couple of tricks that might help you. First of all, if
you can remember that circumference is also found from πD then
you can compare that and find which one matches (2πr). Also, if you
can remember that you learned about circumference before area,
the 2 comes first on the circumference formula, and comes after in
the area formula.
What if I have to find just the area of a slice of pizza,
and not the whole circle?
A:Sector area is easy to find—just like you used its angle to
find the length of an arc, you can use the sector angle to find sector
area. Find the area of the circle then divide it by 360 (to find the
area of a 1 degree sector) and multiply by the angle of your sector.
232 Chapter 5