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How to Compare Slice Sizes on Two Pizzas Using Trigonometry

You can use trigonometry to measure different parts of a circle. For example, say you want to order pizza, but you’re not sure which size to get. You need to know which pizza has bigger slices: a 12-inch pizza cut into six slices, or a 15-inch pizza cut into eight slices.

The following figure shows a 12-inch and a 15-inch pizza that are sliced. Can you tell by looking at them which slices are bigger — that is, have more area?

Sliced pizza — which slices are bigger?
Sliced pizza — which slices are bigger?

The 12-inch pizza is cut into six pieces.

Each piece represents an angle of 60 degrees, which is π/3 radians, so you find the area of each sector (slice) by using the formula for the area of a sector using radians and putting the 6 in for the radius of the pizza with a 12-inch diameter.


(The answer is left with the multiplier of π just so you can compare the sizes between the two pizzas — they’ll both have a multiplier of π in them.)

The 15-inch pizza is cut into eight pieces. Each piece represents an angle of 45 degrees, which is π/4 radians, so, letting the radius be 7.5 this time, the area of each sector is


The π/3 in this formula needs to be π/4.

This result doesn’t tell you exactly how many square inches are in each slice, but you can see that a slice of this 15-inch pizza has an area of 7.03125π square inches, and a slice of the 12-inch pizza has an area of 6π square inches. The 15-inch pizza has bigger pieces, even though you cut it into more pieces than the 12-inch pizza.

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