Question:
In the expansion \({\left( {a – 2b} \right)^8}\), the coefficient of the term containing \({a^4}.{b^4}\) is:
Reference explanation:
Correct answer: A
The general term in the above expansion is
\({T_{k + 1}} = C_8^k. {a^{8 – k}}. {\left( { – 2} \right)^k}. {b^k}\)
Ask the problem to happen when k = 4.
Then the coefficient of the term containing \({a^4}.{b^4}\) is: \(C_8^4{.2^4} = 1120\).
ADSENSE
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