I keep getting “Binomial expansion” questions wrong in Binomial Theorem. What's the trap?
forgetting that the powers of a and b add up to n in every term.
The usual trap: forgetting that the powers of a and b add up to n in every term. How to avoid it: in each term the exponents of a and b sum to n. Go back to the definition — (a+b)^n expands as a sum of terms nCr·a^(n−r)·b^r, with coefficients from Pascal's triangle.
Key point
Binomial expansion
Common mistake
forgetting that the powers of a and b add up to n in every term.
Memory tip
in each term the exponents of a and b sum to n.
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