s="problem">
    A forest ranger needs to estimate the height of a tree. The
    ranger stands 50 feet from the base of tree and measures the
    angle of elevation to the top of the tree to be about
    60$^\circ$. If this angle of 60$^\circ$ is correct, then what
    is the height of the tree? If the ranger's angle measurement
    could be off by as much as $5^\circ$, then how much could his
    estimate of the height be off? Use differentials to give an
    answer.
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