find the positive value of r: 10*pi*r^2+1/2(4/3*pi*r^3)

[aatylenda]

Ok if you didn't catch it the problem is finding the radius of two different cylinders. they both have different radi. the cylinder has a hemisphere at the bottom of it getting the formula 4/3*pi*r^3 the height of the first cylinder is 10 centimeters. the second is 18 centimeters. they both have the same volume of 500 centimeters cubed. So far I have 10*pi*r^2+1/2(4/3*pi*r^3) then put it into the equation 2/3pi r^3+ 10pi r^2 -500=0 then multiply both sides be 3/2s getting pi r^3+15pi r^2 -750=0 please help me if you can I'm really perplexed by this and I've worked on it for hours and asked my parents, brother, sister, and ASK ROSE. please help and thanks to those who tried. Do you think i should use a graphing calculator?? Thanks again Amy Ann

 

[Deleted member 4993]

Ok if you didn't catch it the problem is finding the radius of two different cylinders. they both have different radi. the cylinder has a hemisphere at the bottom of it getting the formula 4/3*pi*r^3 the height of the first cylinder is 10 centimeters. the second is 18 centimeters. they both have the same volume of 500 centimeters cubed. So far I have 10*pi*r^2+1/2(4/3*pi*r^3) then put it into the equation 2/3pi r^3+ 10pi r^2 -500=0 then multiply both sides be 3/2s getting pi r^3+15pi r^2 -750=0 please help me if you can I'm really perplexed by this and I've worked on it for hours and asked my parents, brother, sister, and ASK ROSE. please help and thanks to those who tried. Do you think i should use a graphing calculator?? Thanks again Amy Ann

There are numerical methods involving calculus (Newton-Raphson method) to solve the equation. However, if you have graphing calculator - using that is perfectly legitimate.