A cylinder has a diameter of 9cm and a height of 25cm. What is the surface area of the cylinder if it has a top and a base?
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$\begingroup$In order to find the surface area of a cylinder, add the areas of the two circles on the top and bottom, and the surface area of the side.
(For the surface area of the side, think about the circumference of a circle)
The top and the bottom each have area $\pi(9/2)^2$.
For the rest, use a can opener to remove the top and bottom of the can. Then use metal shears to cut straight down, and flatten out the metal. We get a rectangle of height $25$, and width the circumference of the top. So the width is $9\pi$, and therefore the area of the rectangle is $(9\pi)(25)$.
$\endgroup$ $\begingroup$Surface area of a cylinder = $2\cdot\pi\cdot r^2$ (area of top and bottom) + $\pi\cdot2r\cdot h$ (r=radius, h=height)
Your cylinder has a radius of $4.5$ cm and a height of 25 cm. Should be simple to plug your values into the formula and solve.
$\endgroup$ $\begingroup$Well, the surface area of a cylinder is $A = 2 \pi r^2$.
However, a cylinder isn't only made up of two circles, it is also made up of a rectangle.
Therefore, you must do length times width to find the area of the rectangular shape.
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