If the coefficient of $x^3$ and $x^4$ in the expansion of $(4+k x)^7$ are equal, then the value of $

Question

If the coefficient of $x^3$ and $x^4$ in the expansion of $(4+k x)^7$ are equal, then the value of $k$ is

Professor PC Thomas Classes · Answer

$\binom{7}{3} 4^4 k^3 = \binom{7}{4} 4^3 k^4 \implies k = 4$.