Precalculus

Binomial Expansion

The binomial theorem expands (ax + b)ⁿ into a sum of terms, each with a binomial coefficient C(n, k). This calculator computes every term, multiplies out the powers and collects the result into a polynomial in x.

Binomial Expansion

Expand (ax + b)ⁿ with the binomial theorem.

Try:
Answerx⁴ + 8x³ + 24x² + 32x + 16
  1. Binomial(1x + 2)⁴
  2. Term k = 0C(4,0)·(1x)⁴·(2)⁰ = 1x⁴
  3. Term k = 1C(4,1)·(1x)³·(2)¹ = 8x³
  4. Term k = 2C(4,2)·(1x)²·(2)² = 24x²
  5. Term k = 3C(4,3)·(1x)¹·(2)³ = 32x
  6. Term k = 4C(4,4)·(1x)⁰·(2)⁴ = 16
  7. Expansionx⁴ + 8x³ + 24x² + 32x + 16

Worked examples

Key terms

Frequently asked questions

What is the binomial theorem?

It states that (p + q)ⁿ equals the sum over k of C(n,k)·p^(n−k)·q^k, where C(n,k) is a binomial coefficient.

Where do the coefficients come from?

Each coefficient C(n,k) is a row of Pascal's triangle — the number of ways to choose k factors of q.

Can the exponent be negative or a fraction?

This tool handles whole-number exponents. Negative or fractional exponents give an infinite series, which is a separate topic.