SOLUTION: Between 1989 and 1997 the percentage of households with incomes of $100,000 or more (in 1997 dollars) is modeled by f(x) = .071x2 - .426x + 8.05, where x = 0 represents the year 1

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Question 627543: Between 1989 and 1997 the percentage of households with incomes of $100,000 or more (in 1997 dollars) is modeled by f(x) = .071x2 - .426x + 8.05, where x = 0 represents the year 1989. Based on this model when did the percent of people in this income level reach its minimum?
Answer by ewatrrr(24785) About Me  (Show Source):
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Hi,

f(x) = .071x2 - .426x + 8.05  ||y = ax^2 + bx + c   ⇒ y = a(x -(-b/2a)^2) - a(-b/2a)^2 + c

 f(x) = .071(x-3)^2 - .071·9 + 8.05 

 f(x) = .071(x-3)^2  + 7.411  Vertex(minimum point) is (3,7.411)

Based on this model when did the percent of people in this income level reach its minimum?  1989 + 3 = 1992