maths question

a)　　ES² = 4² - d²
　　　ER² = 3² - d²

　　　The required area is πES² - πER²
　　　= π(16-d²) - π(9-d²)
　　　= 7π cm²

b)　　Volume = base X height = 7πX2X3 = 42π cm³

c)　　(4/3)π(4)³ - 42π = (256/3 - 42)π = (130/3)π cm³

2014-03-28 22:01:28 補充：
Sorry! part c is wrong.

It should be [(4/3)π(4)³ - 42π - (4/3)π(3)³](1/2) =

=[(256/3)π - 42π - 36π]/2

=(11/3)π cm³