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posted by Shane Tuesday, August 6, 2013 at 11:50pm.
In the expansion of (1-2x)^11 the coefficient of x^3 is k times the coefficient of x^2. Evaluate k.
(1-2x)^11 = 1 + 11(-2x) + 55(-2x)^2 + 165(-2x)^3 + ... = 1 - 22x + 220x^2 - 1320x^3 + ... so (220)k = -1320 k = -6
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