math

An observer stands 25 feet from the base of a 50 foot flagpole and watches a flag being lowered at a rate of 5 ft/sec. Determine the rare at which the angle of elevation from the observer to the flag is changing at the instant that the flag is 25 ft.

Keep getting like .1 or .2, help apreciated

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  1. elevation angle A = 45 degrees = pi/4 radians

    tan A = h/25
    d tan A/dA = sec^2 A = (1/25) dh/dA
    so
    25 sec^2 A * dA/dt= dh/dt = 5

    dA/dt = (1/5) cos^2 A
    but cos^2 A = 1/2
    dA/dt = .1 radians/second
    So I agrees
    but maybe you want degrees?
    .1 Rad/s( 180 deg/rad) = 18 degrees/second

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  2. oh its in radians

    thanks a bunch, makes more sense :D

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  3. You are welcome ;)

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