The radius of the cone is 7 feet
The given parameters are:
Surface Area, A = 216π
h = 8/3r
The surface area of a cone is:
[tex]A = \pi r(r + \sqrt{h^2 + r^2})[/tex]
So, we have:
[tex]216\pi = \pi r(r + \sqrt{(8/3r)^2 + r^2})[/tex]
Factor out r
[tex]216\pi = \pi r(r + r\sqrt{(8/3)^2 + 1})[/tex]
Evaluate the exponent
[tex]216\pi = \pi r(r + r * 2.85)[/tex]
Evaluate the sum
[tex]216\pi = \pi r(3.85r)[/tex]
Divide both sides by pi
[tex]216 = 3.85r^2[/tex]
Divide both sides by 3.85
[tex]56.10 = r^2[/tex]
Take the square roots of both sides
r = 7 (approximately)
Hence, the radius of the cone is 7 feet
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