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Math Challenge II-A Combinatorics Chapter 6 Question 9
Math Challenge II-A Combinatorics Chapter 6 Question 9:
The answer is (-1)^3 * (6 choose 3). Why is it 6 choose 3 though? I couldn't quite understand the explanation from Mr. Lensmire in the video lecture. I know that the exponent of (y-1/y)^6 is 6, but why is it choose 3? And why is the coefficient of the constant term y^3 * (1/y)^3?