# Find the dimensions of rectangle of perimeter 36cm which will sweep out a volume as large as possible when revolved about one of its sides.

Arun Kumar IIT Delhi
8 years ago
Hi

$\\a+b=18 \\=>V=\pi a^2 b \\=>{dV \over da}={\pi (a^2(18-a)) \over da} \\=>{dV \over da}=\pi (36a-3a^2)=0 \\=>a(12-a)=0 \\=>a=0,12$

I guess 12 is the right answer.

Thanks & Regards, Arun Kumar, Btech,IIT Delhi, Askiitians Faculty