Exercise 39 Page 820

Montell and Derek are finding the surface area of a cylinder with a height of h= 5 centimeters and a radius of r= 6 centimeters.

We are asked to check if either of them is correct. First we will solve it correctly, and then we will analyze their solutions.

Correct Solution

Let's use the formula for the surface area of a cylinder.

Therefore, the surface area of the given cylinder is 132π square centimeters.

Derek's Solution

As we can see, Derek's solution is almost the same as ours. This tells us that his solution is correct.

Montell's Solution

Montell gets an answer S=66π cm^2. It is different from the correct answer. Therefore, he is not correct. However, let's find where he made a mistake.

It appears that Montell used the formula S=π r^2+π rh to find the surface area of the cylinder. But, the correct formula is S=2π r^2+2π rh.