Past Papers’ Solutions | Cambridge International Examinations (CIE) | AS & A level | Mathematics 9709 | Pure Mathematics 1 (P1-9709/01) | Year 2011 | May-Jun | (P1-9709/13) | Q#1

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Question

The coefficient of  in the expansion of  , where is positive, is 90. Find the value of .

Solution

Expression for the Binomial expansion of  is:

We need to expand both terms one-by-one. First we expand

In the given case:

Hence;

Similarly we also need to expand

First rewrite the given expression in standard form.

In the given case:

Hence;

Now

Since coefficient of  is 90;

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