You didn't finish the question but I assume that you mean the surface area minus the area of the dimples.
The surface area of a sphere is 4π*r^2 and since the diameter is 4.1 cm, the radius is half of that or 2.05 cm.
Hence the surface area of a sphere of radius 2.05 = 4*π*(2.05)^2 =52.8101725 cm^2
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Now for the dimples. They are circles taken out of the surface of the sphere and hence each has an area of π*r^2 and there are 150 of these.
One cm is 10 mm (cm is hundredth, mm is thousandth)
So the radius of the dimples is 0.2cm
150 * π * (0.2)^2 = 150 * π * (0.04) = 6πcm^2 = 18.8495556 cm^2
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Now we subtract the area of the dimples from the area of the sphere:
52.8101725 cm^2
18.8495556 cm^2
------------------------------- Subtract
33.9606165 cm^2
ANSWER: 33.9606165 cm^2 is the surface area of the Golf ball minus the area of the dimples.
Double the Radius to Calculate the Diameter.
You divide the diameter by 2, to get the radius. Then you use the formula for the surface area of a sphere. Surface area of a sphere = 4*pi*radius^2
diameter = 2 * radius
Radius of a circle = diameter/2
You need to know the radius/diameter or the height of the drum.
A radius of a sphere is the distance from its centre to its surface. It is also half of the diameter. If you know the circumference of a circle, you can calculate its radius. Circumference divided by Pi divided by 2 = radius.
The radius of a circle is half of its diameter.
Radius of a circle = diameter/2
to calculate circumference you find a circles radius or diameter. you do diameter times pi or radius times 2 times pi. the you have circumference!
If the diameter is 25 then the radius must be 12.5
You can either measure it, or calculate it if you know the diameter (radius = diameter / 2), or the circumference (radius = circumference / (2pi)).
If you know the circumference, the ration of the diameter to the circumference is π, so diameter = circumference/π If you have the radius, diameter = 2 x radius