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30. If [tex]\(0 \ \textless \ x \ \textless \ 1\)[/tex], then which one of the following is the maximum of [tex]\((x-1)^2 + x\)[/tex]?

A. -1
B. 0
C. 1
D. 2


Sagot :

To find the maximum value of the function [tex]\((x-1)^2 + x\)[/tex] within the interval [tex]\(0 < x < 1\)[/tex], let's go through the solution step by step:

1. Define the function:
[tex]\[ f(x) = (x - 1)^2 + x \][/tex]

2. Find the critical points:
To find the critical points, we first need to take the derivative of the function [tex]\(f(x)\)[/tex].

[tex]\[ f'(x) = \frac{d}{dx}\left[(x-1)^2 + x\right] \][/tex]

Using the chain rule and power rule:

[tex]\[ f'(x) = 2(x - 1) \cdot 1 + 1 = 2(x - 1) + 1 = 2x - 2 + 1 = 2x - 1 \][/tex]

3. Set the derivative equal to zero to find critical points:

[tex]\[ 2x - 1 = 0 \implies x = \frac{1}{2} \][/tex]

Since [tex]\(0 < x < 1\)[/tex], [tex]\(x = \frac{1}{2}\)[/tex] is within the interval.

4. Evaluate the function at the critical points and boundaries:
We need to evaluate the function [tex]\(f(x)\)[/tex] at [tex]\(x = \frac{1}{2}\)[/tex], and also at the boundaries [tex]\(x = 0\)[/tex] and [tex]\(x = 1\)[/tex].

- At [tex]\(x = \frac{1}{2}\)[/tex]:
[tex]\[ f\left(\frac{1}{2}\right) = \left(\frac{1}{2} - 1\right)^2 + \frac{1}{2} = \left(-\frac{1}{2}\right)^2 + \frac{1}{2} = \frac{1}{4} + \frac{1}{2} = \frac{3}{4} \][/tex]

- At [tex]\(x = 0\)[/tex]:
[tex]\[ f(0) = (0 - 1)^2 + 0 = 1 + 0 = 1 \][/tex]

However, note the question specifies [tex]\(0 < x < 1\)[/tex], so we don't include this point for maximizing within the strict interval. Let's just formally note that [tex]\(x=0\)[/tex] would yield [tex]\(f(0)=1\)[/tex].

- At [tex]\(x = 1\)[/tex]:
[tex]\[ f(1) = (1 - 1)^2 + 1 = 0 + 1 = 1 \][/tex]

5. Compare the values to find the maximum:
[tex]\[ f\left(\frac{1}{2}\right) = \frac{3}{4} \][/tex]
[tex]\[ f(0) = 1 \][/tex]
[tex]\[ f(1) = 1 \][/tex]

Thus, the maximum value of the function within the interval [tex]\(0 < x < 1\)[/tex] is [tex]\(\boxed{1}\)[/tex].

Hence the correct answer is:
c. 1