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The population of Japan, 
p, in millions of people at time 
t, where negative values of 
t represent a number of years before January 
1^("st "), 2000 and positive values of 
t represent a number of years after January 
1^("st "),2000 is projected as:

p=128-0.012(t-9.17)^(2)
According to this projection, during which year does Japan reach its maximum population?

The population of Japan, p p , in millions of people at time t t , where negative values of t t represent a number of years before January 1st  1^{\text {st }} , 20002000 and positive values of t t represent a number of years after January 1st ,2000 1^{\text {st }}, 2000 is projected as:\newlinep=1280.012(t9.17)2 p=128-0.012(t-9.17)^{2} \newlineAccording to this projection, during which year does Japan reach its maximum population?

Full solution

Q. The population of Japan, p p , in millions of people at time t t , where negative values of t t represent a number of years before January 1st  1^{\text {st }} , 20002000 and positive values of t t represent a number of years after January 1st ,2000 1^{\text {st }}, 2000 is projected as:\newlinep=1280.012(t9.17)2 p=128-0.012(t-9.17)^{2} \newlineAccording to this projection, during which year does Japan reach its maximum population?
  1. Population Projection Function: The given population projection function is:\newlinep=1280.012(t9.17)2p = 128 - 0.012(t - 9.17)^2\newlineTo find the year when Japan reaches its maximum population, we need to identify the vertex of the parabola represented by this function, since the vertex will give us the maximum value of pp.
  2. Identifying Parabola Vertex: The function is in the form of a parabola with a negative coefficient for the squared term, which means it opens downwards. The maximum value of pp occurs at the vertex of the parabola.\newlineThe vertex form of a parabola is given by:\newlinep=a(th)2+kp = a(t - h)^2 + k\newlinewhere (h,k)(h, k) is the vertex of the parabola.
  3. Comparing with Vertex Form: Comparing the given function with the vertex form, we can see that h=9.17h = 9.17 and k=128k = 128. Since the coefficient aa is negative (0.012-0.012), the vertex represents the maximum point of the parabola.
  4. Finding Maximum Population Time: The vertex (h,k)(h, k) corresponds to the time t=ht = h and the maximum population p=kp = k. Therefore, the maximum population occurs at t=9.17t = 9.17 years.
  5. Calculating Actual Year: To find the actual year when the maximum population is reached, we need to add the value of tt to the base year, which is 20002000.
    Year of maximum population = 2000+t2000 + t
    Year of maximum population = 2000+9.172000 + 9.17
  6. Calculating Actual Year: To find the actual year when the maximum population is reached, we need to add the value of tt to the base year, which is 20002000.
    Year of maximum population = 2000+t2000 + t
    Year of maximum population = 2000+9.172000 + 9.17Calculating the year:
    Year of maximum population 2000+9.17\approx 2000 + 9.17
    Year of maximum population 2009.17\approx 2009.17
    Since we count full years, we round down to the nearest whole year.
    Year of maximum population = 20092009

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