Question

MASSIVE DROP 100 POINTS

Please help me I don't understand

Answer 1

they other person is right!

Answer 2

well, for 3)

we have a cylinder with a hole in it, mind you that we don't have a height for it, so let's call our height "h".

so hmmm let's take the area of the circular rings atop and bottom, Check the picture below. Then we'll take the lateral area of the cylinder.

now, we have a hole in the middle, a cylindrical hole, since we need the walls of that hole, that's simply just the area of the inner-cylinder.

`\stackrel{ \textit{\LARGE area of the outer part} }{\stackrel{ \textit{two circular rings} }{(2)\pi (\stackrel{ R^2 }{10^2} - \stackrel{ r^2 }{5^2})}~~ + ~~\stackrel{ \textit{lateral area} }{2\pi (10)(h)}}\implies 75\pi +20\pi h \\\\[-0.35em] ~\dotfill`

`\stackrel{ \textit{\LARGE area of the inner part} }{\stackrel{ \textit{total area of inner cylinder} }{2\pi (5)(h+5)}\implies 10\pi h+50\pi} \\\\[-0.35em] ~\dotfill\\\\ (75\pi +20\pi h)~~ + ~~(10\pi h+50\pi)\implies {\Large \begin{array}{llll} 125\pi +30\pi h \end{array}}`