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The shape of a colony of bacteria on a Petri dish is circular. Find the approximate increase in its area if its radius increases from 40 mm to 49 mm.

The estimated change in area is nothing mm2.

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  1. A = πr^2
    ∆A ≈ dr ∆r = 2π*40*(49-40) = 720π

    actual change is π(49^2 - 40^2) = 801π
    not very close, since ∆r is so big.

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