Answer: 1570 square inches
This value is approximate since pi = 3.14 is approximate.
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Work Shown:
r = radius = diameter/2 = 20/2 = 10 inches
L = slant height = 40 inches
SA = surface area of the cone
[tex]\text{SA} = \pi*r^2 + \pi*r*L\\\\\text{SA} = \pi*10^2 + \pi*10*40\\\\\text{SA} = \pi*100 + \pi*400\\\\\text{SA} = 100\pi + 400\pi\\\\\text{SA} = (100+400)\pi\\\\\text{SA} = 500\pi \text{ ... exact surface area in terms of pi}\\\\\text{SA} \approx 500*3.14\\\\\text{SA} \approx 1570\\\\[/tex]
The surface area of the cone is approximately 1570 square inches.
We can abbreviate "square inches" into [tex]\text{in}^2[/tex]
If you want to get a more accurate surface area value, then use more decimal digits of pi.
