HELP!!!!!!! A falling object travels a distance given by the formula d=3t+5t2, where d is measured in feet and t is measured in second

Question

HELP!!!!!!!
A falling object travels a distance given by the formula d=3t+5t2, where d is measured in feet and t is measured in seconds. How many seconds will it take for the object to travel 84 feet?

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Hưng Khoa 4 years 2021-08-01T04:33:48+00:00 1 Answers 13 views 0

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    0
    2021-08-01T04:35:20+00:00

    Answer:

    Approximately 3.81 seconds

    Step-by-step explanation:

    d = 3t + 5t²

    d = 84

    84 = 3t + 5t²

    3t + 5t² – 84 = 0

    5t² + 3t – 84 = 0

    5(t² + 3/5t – 84/5) = 0

    5(((t + 3/10)² – 9/100) – 84/5) = 0

    5((t + 3/10)² – 9/100 – 84/5) = 0

    5((t + 3/10)² – 9/100 – 1680/100) = 0

    5((t + 3/10)² – 1689/100) = 0

    5(t + 3/10)² – 1689/20 = 0

    5(t + 3/10)² = 1689/20

    (t + 3/10)² = 1689/100

    t + 3/10 = ±√(1689)/10

    t = -3/10 ± √(1689)/10

    t = -3/10 ± ≈41.1/10

    t = -3/10 ± ≈4.11

    t ≈ -0.3 ± 4.11

    t [can only be positive] ≈ 4.11 – 0.3

    t ≈ 3.81

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