This is a good explanation about how to calculate the surface area of a cylinder. However, it assumes you know how to find the area of a circle and the area of a rectangle. If you don't, please review those concepts before watching this video.
Even if a cylinder looks tall, its circumference can often be larger than its height.
When you flatten out the surfaces of a cylinder, you get two circles and a rectangle.
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surface area of cyclinder
how to calculate surface area of cylinder