Mathematics
Grade10
Easy

Question

If the general term is 91C2 x89, what is the expansion?

  1. (x)91
  2. (x – 2)90
  3. (x – 1)91
  4. (x + 1)90

The correct answer is: (x – 1)91


    STEP BY STEP SOLUTION

    The general term of an expansion is nCr xn – r yr.

    Clearly, here n is 91, and the first term is x raised to the power 89.

    The second term is raised to power 2.

    y2 = 1

    y = +1 or -1

    Therefore, the expansion can either be (x + 1)91 or (x – 1)91.

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