Homework Help: math

Posted by HELP HELP HELP MNHS on Friday, January 11, 2013 at 6:46am.

The illumination a surface receives from a light source varies inversely with the square of the distance. A table lamp is 3ft from a certain work area. How far is another work area if it receives only 1/3 as much illumination as the first work area?

(W/ solution please, tnx...)

math - Reiny, Friday, January 11, 2013 at 8:27am
"The illumination a surface receives from a light source varies inversely with the square of the distance."
-----> I = k(1/d^2) , where I is the illumination, and d is the distance

or:

I1/I2 = d2^2/d1^2

I/(1/3)I) = 3^2 / d1^2

3 = 9/d^2
3d^2= 0
d^2 = 3
d = √3

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