Question 1: Solved
Find the lateral(side) surface area of the cone generated by revolving the line segment y = x/2, 0<= x <= 4, about the x-axis.
i got (pi*sqrt5)/2 just like the image however the answer is 4pi*sqrt5
now when i looked at the image they multiply my answer with
my question is how did they get that and why did they multiply it into the answer...
Question 2: how do i get
in terms of y =
and find the derivative of it