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Mobius - MAT-140-H3778 Precalculus 22EW3
m Southern New Hampshire University-2-1 Discussion: Surface Ares
Part a: Assume that the height of your cylinder is 8 inches. Consider A as a function of r, so we can
write that as A (r) = 2 #r2 + 16 r. What is the domain of A (r)? In other words, for which values of
ris A (r) defined?
Part b: Continue to assume that the height of your cylinder is 8 inches. Write the radius r as a function
of A. This is the inverse function to A (r), ie to turn A as a function of r into. r as a function of A.
a
T(A) =
Hints:
• To calculate an inverse function, you need to solve for r. Here you would start with
A=2 #r2 + 16 r. This equation is the same as 2 r2 + 16 T - A=0 which is a quadratic
equation in the variable r, and you can solve that using the quadratic formula.
3+1
• If you want to type in 2+1 in Mobius, in text mode you can type in (3*pi+1)/(x+1). There is
more information in the Introduction to Mobius unit.
Part e: If the surface area is 275 square inches, then what is the rardius r? In other words, evaluate
r (275). Round your answer to 2 decimal places.
Hint: To compute a numeric square root such as 17.3, you could
• Use a spreadsheet such as Microsoft Excel or OpenOffice Calc and type in Esqrt(173)
• Use a browser to connect to the Internet and type in sqrt(17.3) into a search field
• Use a calculator