College Algebra / Unit 9 Alg 524 short lesson, about 20 seconds
A Single Term of an Expansion
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The idea
One term of (a + b)ⁿ can be written without expanding: the term containing bᵏ is C(n, k)·aⁿ⁻ᵏ·bᵏ.
In practice
The b³ term of (a + b)⁵ is C(5, 3)·a²·b³ = 10a²b³ — one term fetched alone, with no neighboring terms computed.
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