JEE MainMathematicsSequences and SeriesMCQ+4 / −1
Let be an A.P. If , the product is minimum and the sum of its first terms is zero, then is equal to :
- A24
- B
- C9
- D
View written solutionFree
Correct answer: A
- Write the A.P. in standard form
Let the A.P. have first term and common difference . Then
Given:
Also,
We are told this product is minimum.
- Use the condition for minimum product
From (1),
So,
Expand:
This is a quadratic in with positive coefficient, so its minimum occurs at
Then
Hence the A.P. is
- Use the condition that sum of first terms is zero
Sum of first terms of an A.P. is
Given . Since ,
Substitute and :
- Find
First compute:
So we need .
Using
Thus,
- Evaluate the required expression
The printed expression is . With ,
So the value is
- Check with options
Option A is .
So the correct answer is A.
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