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It’s Pi Day. Here, Do Some Math While Looking at (a Frankly Absurd Amount of) Pie.

March 14 has been dubbed Pi Day, thanks to the date’s resemblance to the first few digits of pi, the mathematical symbol that stands for 3.14159 (etc.). Pi, which can be used to calculate various geometric features of a circle, is also obviously a homophone to pie, perhaps explaining people’s willingness to celebrate the contrived holiday.

Pi Day is surprisingly controversial among math geeks. The discontent comes from how the math celebration has, in practice, and especially on the internet, become a day to celebrate pie over pi. The two aren’t wholly unrelated of course; pie is circular, and if you wanted to measure its circumference or area, that’s where good old pi would come in. But something tells me most of the bakers out there aren’t doing much geometry. What a shame.

In a bid to put the pi back in Pi Day, below are some math problems involving pi. (Each problem is linked to its source.) We’ve paired them with a bunch of photos from Pie Instagram, because it turns out there is a delightful community of bakers there. By using Pi Day as an excuse to post a bunch of cool pie photos, are we part of the problem? Maybe. Oh well, and happy Pi Day!

A circular pizza costs $19.99. What is the cost of 1 square centimeter if the diameter of the pizza is 36 cm?

Write the equation of the circle with center at (0, 0) and a radius of 6.

If the diameter of a circle is 9 centimeters, then what is the area? 

The radius of circular disk is increased by 20 percent. What is the percent increase in the area of the disk?

Find the center and radius of the circle whose equation is given by: (x - 2)2 + (y + 5)2 = 13.

A circular table has a diameter of 100 inches. A circular tablecloth hangs over the table 15 inches around the table. What is the area of the tablecloth? 

Find the center and radius of the circle whose equation is given by: x2 + y2 + 6x - 10y = 9.

A water sprinkler can spray water at a maximum distance of 12 meters in all directions. What area of the garden can this sprinkler irrigate? Round your answer to the nearest square meter. 

Find the equation of a circle that has a diameter with end points (-6 , 1) and (2 , -5).

Find the diameter of a circle with a circumference of 21.98 meters.

Find the point of intersection of the circle with equation (x - 2)2 + y2 = 8 and the line with equation y = x – 2.

Find the equations of the circle with center at (-3 , 5) that passes through the point (5 , -1).