WAEC - Further Mathematics (2008 - No. 19)
The coefficient of the 5th term in the binomial expansion of \((1 + kx)^{8}\), in ascending powers of x is \(\frac{35}{8}\). Find the value of the constant k.
2
\(\frac{1}{2}\)
\(-\frac{1}{2}\)
-2
Explanation
\((1 + kx)^{8} = ^{8}C_{0}(1^{8})(kx)^{0} + ^{8}C_{1}(1^{7})(kx)^{1} + ...\)
The 5th term = \(^{8}C_{5 - 1}(1^{4})(kx)^{4}\)
= \(^{8}C_{4} (kx)^{4}\)
\(\implies 70k^{4} = \frac{35}{8}\)
\(k^{4} = \frac{\frac{35}{8}}{70}\)
\(k^{4} = \frac{1}{16}\)
\(k = \frac{1}{2}\)
Comments (0)
