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Printjmc
geometry junior
Problem
A cylinder has a height of and a radius of Determine the total surface area, including the two ends, of the cylinder. 
Solution
To calculate the total surface area of the cylinder, we cut off the two ends to obtain two circles of radius
The two ends combined have an area of Next, we must calculate the lateral surface area. To do this, we make a vertical cut through this area, and unroll the lateral surface. When we do this, we obtain a rectangle with height The width of the rectangle (ie. the length of the top edge) is equal to the circumference of one of the ends, since the top edge of this rectangle lay exactly along the circumference of the top end.
The circumference of one of the ends is so the width of the rectangle is Therefore, the area of this rectangle is So the total surface area of the cylinder is
The two ends combined have an area of Next, we must calculate the lateral surface area. To do this, we make a vertical cut through this area, and unroll the lateral surface. When we do this, we obtain a rectangle with height The width of the rectangle (ie. the length of the top edge) is equal to the circumference of one of the ends, since the top edge of this rectangle lay exactly along the circumference of the top end.
The circumference of one of the ends is so the width of the rectangle is Therefore, the area of this rectangle is So the total surface area of the cylinder is
Final answer
78\pi