Question

Help on solving this question

Answer 1

Step-by-step explanation:

area of the cross section = πr²-π(1/2r)²

$= \pi( {r}^{2} - \frac{ {r}^{2} }{4} )$

$= \pi( \frac{4 {r}^{2} - {r}^{2} }{4})$

$= \pi \frac{3 {r}^{2} }{4}$

option D