Answer:
Look at the unfolded cylinder down: it's consisted of a rectangle and 2 circles. so to find the surface area of the cylinder we should find the areas of the rectangle and the 2 circles.
1) A of 2 circles = 2(π) = 2π
2) A of rectangle = base x height (or length x width) = bh
but the if we fold the rectangle? what will happen?
the base will go around the circle, this means that the base is equal to the circle circumference, which is 2πr.
Therefore, A of rectangle = 2πrh
3) Surface area of cylinder = 2π + 2πrh
simplify more and take the common factor 2πr:
= 2πr (r+h)
