College Algebra

Intensity of Light. The intensity I of light from a light bulb varies inversely as the square of the distance d from the bulb. Suppose that I is
90W/m2 (watts per square meter) when the distance is 5 m. How much farther would it be to a point where the intensity is

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  1. I = k/d^2
    so, Id^2 = k is constant

    So, find d such that

    40d^2 = 90*5^2

    and subtract 5

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