Homework Help: algebra

Posted by ken on Monday, November 1, 2010 at 6:52pm.

a storage bin is shaped like a cylinder with a hemisphere shaped top. the cylinder is 45 inches tall. the volume of the bin is 4131 pi cubic inches. find the radius of the bin.

i think [4(pi)r(cubed)]/3=volume of hemisphere

and h (pi) r squared volume of the cylinder.

so

[4(pi) r (cubed)/3] + [45 (pi) r squared= volume of bin

so

[4 r (cubed)/3] + [45 (pi) r squared=volume

how do i solve for r?

sorry, i'm stuck

algebra - bobpursley, Monday, November 1, 2010 at 6:56pm
the volume of a sphere is 4/3 PI r^3, so a hemisphere would be half of that.

If you have an equation such as this,

a r^3 + b r^2 + c=0

it is a third degree equation. I think I would graph
f(r)= a r^3+b r^2+c and see where it crosses the axis, that is a solution.
There are ways to solve cubic equations, but for this, I would graph it.
algebra - ken, Monday, November 1, 2010 at 7:09pm
thanks Mr. Pursley,
graphing it now.

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