The least value of for which the number of integral terms in the Binomial expansion of is , is:
- A
- B
- C
- D
The least value of for which the number of integral terms in the Binomial expansion of is , is:
Correct answer:C
Standard Method
Given: We need the least value of for which the number of integral terms in the binomial expansion is .
Find: The least integer .
From the solution working, consider the general term of
For to be an integer, both exponents must be integers.
So the conditions are
and
Hence,
for some integer , and must be divisible by .
The number of admissible values is therefore taken as
Given that the number of integral terms is ,
So,
Detailed Counting
Now solve the inequality coming from the floor function:
That is,
Therefore, the least integer value is
So the correct option is C.
Note: The solution works with and concludes . The final answer on the page is C, which matches option .
A common mistake is to count all multiples of without also checking the divisibility condition on . A term is integral only when both exponent conditions are satisfied. Always verify every irrational power becomes an integer power.
Another mistake is to set instead of using the counting formula . The extra appears because counting includes .
Students may choose by taking the upper end of the interval . This is wrong because the question asks for the least value of . Always select the smallest integer satisfying the condition.
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