Given , . Then is equal to:
- A
- B
- C
- D
Given , . Then is equal to:
Correct answer:A
Standard Method
Given:
Find:
Differentiate the given function:
Differentiate again:
And the third derivative is:
Now use the relations shown in the solution:
Substitute these values into the expression for :
Differentiate this simplified form:
Now evaluate at :
Therefore, the correct option is A and .
Using derivative conditions explicitly
Given:
Find:
From the given form,
so at ,
Using from the solution,
which gives
Also,
so at ,
Using ,
This is consistent with the value used above.
Now compute
Hence, , so the correct option is A.
Students may treat , , and as functions of . They are constants because the derivatives are evaluated at fixed points. Differentiate them as constants, not as variable expressions.
A common error is to substitute values into before first identifying derivative relations carefully. First compute , , and correctly, then use the evaluated conditions.
Some students differentiate incorrectly as or . Since is a constant, the derivative is .
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