Haley substituted the values of a, b, and c into the quadratic formula below. x = StartFraction negative (negative 10) plus or minus StartRoot (negative 10) squared minus 4 (7)(negative 2) EndRoot Over 2(7) EndFraction What was Haley’s function in standard form? f(x) = x2 + x +

Where does that StartFraction ... mess come from? -- I've seen it in other questions.

Comparing that to the general quadratic formula

we see b=-10 (agreeing in both places) a=7 (two places), c=-2

7x² - 10x - 2 = 0

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

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