Math Problem Statement

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Trong thí nghiệm y học, người ta cấy 1000 vi khuẩn vào môi trường dinh dưỡng. Bằng thực nghiệm, người ta xác định số lượng vi khuẩn thay đổi theo thời gian bởi công thức \( N(t) = 1000 + \frac{100t}{100 + t^2} \). Tính số lượng vi khuẩn lớn nhất kể từ khi thực hiện cấy vi khuẩn vào môi trường dinh dưỡng.

Solution

To solve this problem, we need to find the maximum value of the function N(t)N(t) that represents the number of bacteria over time, where:

N(t)=1000+100t100+t2N(t) = 1000 + \frac{100t}{100 + t^2}

Here, tt is time in seconds.

Step-by-Step Solution

  1. Identify the Function: The function N(t)=1000+100t100+t2N(t) = 1000 + \frac{100t}{100 + t^2} models the number of bacteria over time.

  2. Find the Derivative N(t)N'(t): To find the maximum value, we need to calculate the first derivative N(t)N'(t) and set it to zero. This will help identify any critical points.

    N(t)=1000+100t100+t2N(t) = 1000 + \frac{100t}{100 + t^2}

    Let f(t)=100t100+t2f(t) = \frac{100t}{100 + t^2}. Then, the derivative f(t)f'(t) can be found using the quotient rule:

    f(t)=(100)(100+t2)(100t)(2t)(100+t2)2f'(t) = \frac{(100)(100 + t^2) - (100t)(2t)}{(100 + t^2)^2}

    Simplifying, we get:

    f(t)=10000+100t2200t2(100+t2)2=10000100t2(100+t2)2f'(t) = \frac{10000 + 100t^2 - 200t^2}{(100 + t^2)^2} = \frac{10000 - 100t^2}{(100 + t^2)^2}

    Therefore,

    N(t)=f(t)=10000100t2(100+t2)2N'(t) = f'(t) = \frac{10000 - 100t^2}{(100 + t^2)^2}

  3. Set N(t)=0N'(t) = 0: To find critical points, set N(t)=0N'(t) = 0:

    10000100t2=010000 - 100t^2 = 0

    t2=100t^2 = 100

    t=±10t = \pm 10

    Since tt represents time in seconds, we only consider t=10t = 10 seconds.

  4. Evaluate N(t)N(t) at t=10t = 10: Substitute t=10t = 10 into N(t)N(t) to find the number of bacteria:

    N(10)=1000+10010100+102N(10) = 1000 + \frac{100 \cdot 10}{100 + 10^2}

    =1000+1000200=1000+5=1005= 1000 + \frac{1000}{200} = 1000 + 5 = 1005

  5. Conclusion: The maximum number of bacteria is 1005.

Would you like a more detailed explanation on any specific part of this solution?


Related Questions

  1. How would the answer change if the function for N(t)N(t) had a different constant added to 1000?
  2. What happens to N(t)N(t) as tt approaches infinity?
  3. Could we calculate the time tt when the bacteria population reaches a certain threshold?
  4. How does the growth rate of bacteria change at different times?
  5. How would we model bacterial growth if it followed a logistic rather than the given formula?

Tip

In optimization problems, always check the boundary values and any critical points to ensure you’ve found the true maximum or minimum.

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Math Problem Analysis

Mathematical Concepts

Optimization
Derivatives
Quotient Rule

Formulas

\( N(t) = 1000 + \frac{100t}{100 + t^2} \)
Quotient Rule: \( f'(x) = \frac{g'(x)h(x) - g(x)h'(x)}{h(x)^2} \)

Theorems

First Derivative Test for Maximum

Suitable Grade Level

Grade 11-12