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Quadratic word problems (standard form)

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Rui is a professional deep water free diver.
His altitude (in meters relative to sea level), x seconds after diving, is modeled by:
d, left parenthesis, x, right parenthesis, equals, start fraction, 1, divided by, 2, end fraction, x, squared, minus, 10, x
How many seconds after diving will Rui reach his lowest altitude?
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text