You are making an umbrella that is shaped like a regular octagonal pyramid.
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Answer:
Step-by-step explanation:
Cost = Area Cylinder body* cost * 0.03 cm^3 + Area of 2 lids*cost 0.06 of cm^3
Volume = 300 cm^3
Volume = Base *h
Volume = pi * r^2 * h = 300
h = 300/(pi * r^2 )
Area material = 2*pi * r * h * 0.03 + 2 pi r^2 * 0.06
Area material = 0.06*pi * r * 300/(pi* r^2) + 0.12 * pi * r^2
dmaterial/dr = (-1)18 r^-2 + 0.12 pi * 2*r
dmaterial/dr = -18 r^-2 + 0.24 pi * r
The minimum occurs when the right side = 0
18/r^2 = 0.24 *pi r
18 = 0.24*pi * r^3
18/(0.24 * pi) = r^3
23.89 = r^3
cube root (23.89) = cuberoot(r^3)
r = 2.88 cm
h = 300/pi * r^2
h = 300/(3.14 * 2.88^2)
h = 11.52
This isn't much of a check but we can try it.
Volume = 3.14 * 2.88^2 * 11.52
Volume = 302.01 which considering all the rounding is pretty close.
Here's a graph that confirms my answer.
