Math CentralQuandaries & Queries


Question from Shannon:

I have a cylinder with a radius of 2' 1 5/8".
How do I calculate the radius increase when I cut the cylinder at a 45 degree angle?

Hi Shannon,

First I would convert the radius to inches in decimal form. I get 25.625 inches.


On the diagram C is in the centre of the cylinder. The triangle ABC is a right triangle and since the measure of the angle CAB is 45 degrees |BC| = |CA| = r, the radius of the cylinder. Using Pythagoras theorem

|BC|2 + |CA|2 = |AB|2


|AB|2 = r2 + r2 = 2r2

and hence |AB| = √2 r = 1.4142 × r.


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