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In the expansion of (1-2x)^11 the coefficient of x^3 is k times the coefficient of x^2. Evaluate k.

  • maths -

    (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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