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A person standing near the edge of a cliff 120 feet above a lake throws a rock upward with an initial speed of 40 feet per second. The height of the rock above the lake at the bottom of the cliff is a function of time and is described by the function H(t) = –16t2 + 40t + 120.
a) How many seconds will it take until the rock reaches its maximum height?
b) What is that height?

  • Math - ,

    H(t) = -16t^2 + 40t + 120

    Finding critical point...

    H'(t) = -32t + 40 ...... Differentiation
    0 = -32t + 40
    32t = 40
    t = 1.25 seconds

    Thats you answer for (a). Use it to find the answer for (b).

  • Math - typo - ,

    Thats you...

    I meant "that's your..."

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