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if f(x) is a differential function such ...

if `f(x)` is a differential function such that `f(x)=int_(0)^(x)(1+2xf(t))dt&f(1)=e`, then
Q. Identify the correct statements (s):

A

`f(x)` is an even function

B

`f(x)` is an odd function

C

`f(x)` is always increasing function

D

`f(x)` is always decreasing function

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The correct Answer is:
To solve the problem step by step, we start with the given information about the function \( f(x) \): 1. **Given Function**: \[ f(x) = \int_0^x (1 + 2x f(t)) dt \] and \( f(1) = e \). 2. **Rearranging the Integral**: We can rewrite the function as: \[ f(x) = \int_0^x 1 \, dt + \int_0^x 2x f(t) \, dt \] The first integral evaluates to \( x \): \[ f(x) = x + 2x \int_0^x f(t) \, dt \] 3. **Isolate the Integral**: Rearranging gives: \[ f(x) - x = 2x \int_0^x f(t) \, dt \] Dividing both sides by \( 2x \) (assuming \( x \neq 0 \)): \[ \frac{f(x) - x}{2x} = \int_0^x f(t) \, dt \] 4. **Differentiate Both Sides**: Now, we differentiate both sides with respect to \( x \): \[ \frac{d}{dx}\left(\frac{f(x) - x}{2x}\right) = \frac{d}{dx}\left(\int_0^x f(t) \, dt\right) \] Using the quotient rule on the left side: \[ \frac{(f'(x) - 1) \cdot 2x - (f(x) - x) \cdot 2}{(2x)^2} = f(x) \] Simplifying gives: \[ (f'(x) - 1) \cdot x - (f(x) - x) = x^2 f(x) \] 5. **Rearranging the Equation**: This leads to: \[ x f'(x) - f(x) = x^2 f(x) + x \] Rearranging yields: \[ x f'(x) = (x^2 + 1) f(x) + x \] 6. **Expressing \( f'(x) \)**: Thus, we can express \( f'(x) \) as: \[ f'(x) = \frac{(x^2 + 1) f(x) + x}{x} \] 7. **Finding the General Solution**: To solve this differential equation, we can separate variables: \[ \frac{f'(x)}{f(x)} = \frac{x^2 + 1}{x} + \frac{1}{x} \] Integrating both sides gives: \[ \ln |f(x)| = \frac{x^2}{2} + \ln |x| + C \] Therefore: \[ f(x) = k \cdot x \cdot e^{\frac{x^2}{2}} \] where \( k = e^C \). 8. **Using the Initial Condition**: We know \( f(1) = e \): \[ f(1) = k \cdot 1 \cdot e^{\frac{1^2}{2}} = k \cdot e^{\frac{1}{2}} = e \] Solving for \( k \): \[ k = e^{1 - \frac{1}{2}} = e^{\frac{1}{2}} = \sqrt{e} \] 9. **Final Form of \( f(x) \)**: Thus, we have: \[ f(x) = \sqrt{e} \cdot x \cdot e^{\frac{x^2}{2}} = x \cdot e^{\frac{x^2}{2} + \frac{1}{2}} \] 10. **Identifying the Properties of \( f(x) \)**: - Since \( e^{\frac{x^2}{2}} \) is always positive and increasing, \( f(x) \) is an increasing function. - To check if \( f(-x) = -f(x) \), we find: \[ f(-x) = -x \cdot e^{\frac{x^2}{2} + \frac{1}{2}} = -f(x) \] Thus, \( f(x) \) is an odd function. ### Conclusion: The correct statements about \( f(x) \) are: - \( f(x) \) is an increasing function. - \( f(x) \) is an odd function.
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