WAEC - Further Mathematics (2007 - No. 10)
Find the fourth term of the binomial expansion of \((x - k)^{5}\) in descending powers of x.
\(10x^{3}k^{2}\)
\(5x^{3}k^{2}\)
\(-5x^{2}k^{3}\)
\(-10x^{2}k^{3}\)
설명
\((x - k)^{5} = ^{5}C_{0}x^{5}(-k)^{0} + ^{5}C_{1}x^{4}(-k)^{1} + ...\)
The fourth term in the expansion = \(^{5}C_{4 - 1}(x)^{5 - 3}(-k)^{3 = 10 \times x^{2} \times -k^{3}\)
= \(-10x^{2}k^{3}\)