If the function is differentiable on , then is equal to:
JEE Mathematics 2024 Question with Solution
Answer
Correct answer:15
Step-by-step solution
Standard Method
Given: The piecewise function is
and it is differentiable on .
Find: The value of .
For differentiability, the function must be both continuous and differentiable at the boundary points and .
Using continuity at :
Using continuity at gives the same equation:
Now differentiate each part:
Using differentiability at :
Using differentiability at also gives the same value:
Substitute into the continuity equation:
Now compute:
Therefore, the value of is .
Continuity and Differentiability at Both Junctions
Given: The definition changes at , so the critical points are and .
Find: Determine and , then evaluate .
At , continuity requires
At , continuity requires
So continuity gives the single equation
For differentiability at :
For differentiability at :
This confirms the same value of .
Now solve for :
Finally,
Hence, the required numerical value is .
Common mistakes
Checking only continuity and not differentiability at is incorrect, because the question explicitly says the function is differentiable on . After matching function values, also equate the derivatives from both sides.
Differentiating incorrectly near negative values is a common error. For , , so , whose derivative is .
Using the wrong derivative for the positive branch at leads to sign mistakes. Since there, the derivative is , not .
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