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The radius of a right circular cone is increasing at a rate of 1.6 in/s while its height is decreasing at a rate of 2.4 in/s. At what rate is the volume of the cone changing when the radius is 129 in. and the height is 128 in.?

Respuesta :

Answer:

Explanation:

[tex]\frac{dr}{dt}[/tex] = 1.6in/s, [tex]\frac{dh}{dt}[/tex] = -2.4 in/s radius = 129 in and height = 128 in

the volume of a right circular cone = [tex]\frac{1}{3} \pi r^{2} h[/tex]

using chain rule equation to determine the rate of change in volume

[tex]\frac{dv}{dt}[/tex] = [tex]\frac{dv}{dr}[/tex] ([tex]\frac{dr}{dt}[/tex]) + [tex]\frac{dv}{dh}[/tex]( [tex]\frac{dh}{dt}[/tex])

partial differentiating with respect to radius and height respectively

[tex]\frac{dv}{dr}[/tex] = [tex]\frac{d}{dr}[/tex]( [tex]\frac{1}{3}\pi r^{2} h[/tex]) = [tex]\frac{2}{3}\pi rh[/tex] = 11008 π

[tex]\frac{dv}{dh}[/tex] = [tex]\frac{d}{dh}[/tex]([tex]\frac{1}{3}\pi r^{2} h[/tex]) = [tex]\frac{1}{3}\pi r^{2}[/tex] = 5547π

[tex]\frac{dv}{dt}[/tex]  = 11008 π(1.6 in/s) + 5547π (-2.4in/s) = 4300π in³ / s