
Formula Derivation Expansion and Solved Examples
FAQs on Binomial Theorem for Positive Integral Indices Explained
1. What is the Binomial Theorem for positive integral indices?
The Binomial Theorem for positive integral indices states that for any positive integer n, (a + b)n = Σ [nCr · an−r br], where r = 0 to n.
- nCr = n! / (r!(n−r)!)
- The expansion contains n + 1 terms
- Each term is called a binomial term
2. What is the formula for the general term in a binomial expansion?
The general term in the expansion of (a + b)n is Tr+1 = nCr · an−r br.
- Here, r = 0, 1, 2, ..., n
- nCr is the binomial coefficient
- Tr+1 represents the (r+1)th term
3. How do you expand (a + b)n using the Binomial Theorem?
To expand (a + b)n, apply the formula (a + b)n = Σ [nCr · an−r br].
- Write binomial coefficients nC0 to nCn
- Reduce the power of a from n to 0
- Increase the power of b from 0 to n
4. What are binomial coefficients in the Binomial Theorem?
Binomial coefficients are the numerical factors nCr = n! / (r!(n−r)!) in the binomial expansion.
- They determine the weight of each term
- They are symmetric: nCr = nC(n−r)
- They appear in Pascal’s Triangle
5. How many terms are there in the expansion of (a + b)n?
The expansion of (a + b)n contains exactly n + 1 terms.
- The first term corresponds to r = 0
- The last term corresponds to r = n
- Each successive term changes powers systematically
6. Can you give an example of binomial expansion for a positive integer?
Yes, for example, the expansion of (x + y)3 is x3 + 3x2y + 3xy2 + y3.
- Coefficients: 1, 3, 3, 1
- Total terms: 4
- Powers of x decrease while powers of y increase
7. What is the middle term in a binomial expansion?
The middle term in (a + b)n depends on whether n is even or odd.
- If n is even, there is one middle term: T(n/2)+1
- If n is odd, there are two middle terms
8. What is the difference between permutation and binomial coefficient nCr?
The binomial coefficient nCr represents combinations, while nPr represents permutations.
- nCr = n! / (r!(n−r)!) (order does not matter)
- nPr = n! / (n−r)! (order matters)
9. How is Pascal’s Triangle related to the Binomial Theorem?
Pascal’s Triangle provides the binomial coefficients used in the expansion of (a + b)n.
- Each row corresponds to powers of n
- The entries are nC0, nC1, nC2, ..., nCn
- Each number equals the sum of the two numbers above it
10. What are common mistakes in using the Binomial Theorem?
Common mistakes in the Binomial Theorem include incorrect coefficients, wrong powers, and sign errors.
- Forgetting that powers of a decrease and b increase
- Misapplying the formula for nCr
- Ignoring negative signs in expressions like (a − b)n





















