Question

How do you use the binomial formula to find the coefficient of `u^(4)z^(15)` in the expansion of `(3u+z)^19`?

Answer 1

313956

Explanation:

The coefficient of `a^rb^(n-r)` in the expansion of `( a + b )^n` is `nCn-r` = `(n!)/((n-r)!r!)`

Here a = 3u, b = z, n = 19 and r = 4.

Answer is 19C4 X `3^4` = `3^4`(19.18.17.16(/(1.2.3.4) = 313956.