Discussion

Question:

When ${(1 - \frac{1}{a})}^{6}$ is expanded, the sum of the last three coefficients is:

Explanation:

When ${(1 - \frac{1}{a})}^{6}$ is expanded, the the last three coefficients are:

⁶C₄, −⁶C₅ and ⁶C₆

⁶C₄ = 15
−⁶C₅ = −6
⁶C₆ = 1

∴ The sum of coefficients = 15 – 6 + 1 = 10

Hence, option (c).

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