Notes from Toppers
Binomial Expansions
1. Binomial Theorem
- Formula: (a + b)^n = ∑C(n, r) * a^(n-r) * b^r, where C(n, r) is the binomial coefficient.
- Binomial Coefficients: C(n, r) = n!/(r!(n-r)!)
- Properties:
- Symmetry: C(n, r) = C(n, n-r)
- Pascal’s Triangle: C(n, r) can be represented in the form of Pascal’s triangle.
2. Applications in Combinations and Probability
- Combinations: Binomial expansion is used to count the number of ways to select r objects from a set of n distinct objects.
- Probability: Binomial expansion is used to calculate probabilities in various scenarios, such as the binomial distribution and the normal distribution.
3. Power Series Expansions
- Concept: A power series expansion is an infinite series of terms involving powers of a variable x.
- Examples:
- sin(x) = x - x^3/3! + x^5/5! - …
- cos(x) = 1 - x^2/2! + x^4/4! - …
- e^x = 1 + x + x^2/2! + x^3/3! + …
- ln(1+x) = x - x^2/2 + x^3/3 - …
4. Binomial Approximations
- Approximation: (1+x)^n ≈ 1 + nx when x is small compared to 1.
- Applications:
- Approximating probabilities in the binomial distribution
- Simplifying complex expressions
5. Multinomial Expansions and Generalizations
- Multinomial Theorem: (a + b + c)^n = ∑C(n, r, s) * a^r * b^s * c^t, where C(n, r, s, t) is the multinomial coefficient.
- Multinomial Distribution: The multinomial distribution is a generalization of the binomial distribution for multiple categories.
6. Series involving Binomial Expansions
- Sum of Finite Terms: ∑C(n, r) * a^r * b^(n-r) = (a + b)^n
- Infinite Series: ∑C(n, r) * x^r diverges for |x|>1 and converges for |x|<1.
7. Applications in Calculus
- Derivatives: Binomial expansion can be used to find derivatives of certain functions.
- Integrals: Binomial expansion can be used to find integrals of certain functions.
References:
- NCERT Mathematics, Class 11, Chapter 15:Binomial Theorem
- NCERT Mathematics, Class 12, Chapter 9:Sequences and Series