Expanding $(x-y)^n$

#binomial theorem#sign#expansion

Statement

Expand $(x-y)^3$ .

Hint

$(x-y)^n=\sum_{k}\binom{n}{k}x^{n-k}(-y)^k$ .

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Formula. $(x-y)^3=x^3-3x^2y+3xy^2-y^3$ .

Conclusion. $(x-y)^3=x^3-3x^2y+3xy^2-y^3$ .