Question
The real number for which the equation, has two distinct real roots in
Options
Solution
Key Concepts and Formulas
- Derivative and Monotonicity: If on an interval, then is strictly increasing on that interval. If , then is strictly decreasing.
- Number of Roots: A strictly monotonic function can have at most one real root. For a continuous function to have two distinct real roots in an interval, it must have at least one local extremum within that interval.
- Intermediate Value Theorem (IVT): If is continuous on and is a number between and , then there exists a in such that .
Step-by-Step Solution
Step 1: Define the function and find its derivative. We are given the equation . Let's define the function . We want to find the values of for which has two distinct real roots in the interval . First, we find the derivative of with respect to :
Step 2: Analyze the monotonicity of the function. Now, we analyze the sign of . Since for all real numbers , we have . Therefore, . This means for all . Since for all , the function is strictly increasing on the entire real line, and in particular, on the interval .
Step 3: Determine the possible number of roots. Because is strictly increasing, it can have at most one real root. Therefore, it is impossible for to have two distinct real roots in the interval .
Step 4: Conclusion Since the function is strictly increasing, it can have at most one root. Therefore, there is no value of for which the given equation has two distinct real roots in the interval .
Common Mistakes & Tips
- Misinterpreting Monotonicity: A common mistake is to assume that a function with a derivative that is always positive must have a root. A strictly increasing function can lie entirely above or entirely below the x-axis.
- Forgetting the Definition of Distinct Roots: Remember that distinct roots must be different from each other.
- Checking for Local Extrema: When looking for multiple roots, always check for local maxima or minima within the interval of interest.
Summary
We analyzed the function by finding its derivative and determining its monotonicity. Since the derivative is always positive, the function is strictly increasing, meaning it can have at most one real root. Therefore, there is no value of for which the equation has two distinct real roots in the interval .
Final Answer The final answer is \boxed{does not exist}, which corresponds to option (D).