Solution
To find the absolute minimum value of the function f(x)=10x(2−lnx) on the interval [1,e2], we follow these steps:
Step 1: Find the derivative of f(x)
We need to differentiate the function f(x)=10x(2−lnx).
First, apply the product rule:
f′(x)=dxd[10x]⋅(2−lnx)+10x⋅dxd(2−lnx)
f′(x)=10(2−lnx)+10x⋅(−x1)
f′(x)=10(2−lnx)−10
f′(x)=20−10lnx−10
f′(x)=10(1−lnx)
Step 2: Find the critical points
Set the derivative equal to zero to find the critical points:
10(1−lnx)=0
1−lnx=0
lnx=1
x=e
Step 3: Evaluate the function at the critical points and endpoints
We now evaluate f(x) at the critical point x=e and at the endpoints of the interval [1,e2].
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At x=1:
f(1)=10⋅1⋅(2−ln1)=10⋅1⋅(2−0)=20
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At x=e:
f(e)=10⋅e⋅(2−lne)=10⋅e⋅(2−1)=10e
Since e≈2.718, 10e≈27.18.
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At x=e2:
f(e2)=10⋅e2⋅(2−lne2)=10⋅e2⋅(2−2)=0
Step 4: Determine the absolute minimum
Among the values computed:
- f(1)=20
- f(e)≈27.18
- f(e2)=0
The absolute minimum value of f(x) on the interval [1,e2] is 0 at x=e2.