On page 31 CS1-04 2021/22 Core reading materials. The summation of x=0 to z of (zCx)lambda^x * mu^(z-x) returns to (lambda +mu)^z How is this arrived at? any references to the notes?
The formula given in the penultimate line of the equation is the binomial expansion of (lambda + mu)^z. The binomial expansion formula is given on page 2 of the Tables. Here we are replacing a with lambda, b with mu, and n with z.