A circle has radius R cm, where R is uniformly distributed on the interval [4, 10]. The area of the circle is A cm^2. Calculate Var(A).

Question

mathmale · Answer

You begin by stating that the radius of this circle is R cm, but then go on to state that R is uniformly distributed over some given interval.  How's that again?  The radius of a circle is a fixed quantity; it cannot and does not vary.  Are you thinking of the density of the material making up a circular disk?   or?

loinducoeur · Answer

I just keep getting a negative answer for the variance. It should be positive, right?

jhonyy9 · Answer

so than understand your exercise right - Var(A) is direct proportional with var(r) - where r is radius of circle - because you know that area of circle = pi*r^2 so from what result that when the radius varies for example increasing result that area of circle varies too in proportion directly with radius - hope so much that is understandably -

loinducoeur · Answer

I think it's like that, yeah.

loinducoeur · Answer

Thanks for the no help, guys! c: I'll just ask my teacher tomorrow who is evidently more aware of actual stats than you are.

jhonyy9 · Answer

was my pleasure 

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