Respuesta :
f(x) = x - 5 ln(x)
Get the derivative:
f'(x) = 1 - 5/x
Find the critical points:
• f'(x) = 1 - 5/x = 0 -> 5/x = 1 -> x = 5
• f'(x) is undefined for x = 0, but that's outside the domain of f(x)
Get the second derivative:
f''(x) = 5/x ^2
Check the sign of the second derivative at the critical point x = 5:
f'' (5) = 5/5^2 = 5/25 = 1/5 > 0
Since the second derivative is positive at this point, this means x = 5 is a local minimum.
Check the value of f(x) at the critical point as well as the endpoints of the given domain:
f (5) = 5 - 5 ln(5) ≈ -3.407
f (1/5) = 1/5 - 5 ln(1/5) ≈ 1.809
f (10) = 10 - 5 ln(10) ≈ -1.513
So we have
• absolute maximum = 1/5 - 5 ln(1/5) at x = 1/5
• absolute minimum = 5 - 5 ln(5) at x = 5
The absolute maximum value is f(5)=5−5ln(5), and this occurs at x equals 5
The absolute minimum value is f(1/5)= 1/5−5ln(1/5), and this occurs at x equals 1/5
Given the function f(x)=x−5ln(x),
We are to find the absolute minimum and maximum value of the function
At the turning point f'(x) = x - 5ln(x)
f'(x) = 1 - 5/x
0 = 1 - 5/x
-5/x = -1
-x = -5
x = 5
Find the second derivative of the function;
f''(x) = -5/x²
Substitute the value of x = 5 into the second derivative function to have:
f''(5) = -5/5² = 1/5
Since f''(5) = 1/5 < 0, this is the local maximum and the point x = 5 is the absolute minimum
The absolute maximum value is f(5)=5−5ln(5), and this occurs at x equals 5
The absolute minimum value is f(1/5)= 1/5−5ln(1/5), and this occurs at x equals 1/5
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