par(mfrow=c(2,2))

lambda_list<-c(3, 5, 10, 15) # 평균
x_list<-30 # 발생횟수를 1부터 x축에 보여줄 최대값

for (i in 1:length(lambda_list)) {
    p_x<-dpois(x=0:x_list,lambda_list[i])
    plot(x=0:x_list, p_x, xlab="x", ylab="P(X=x)", ylim=c(0, 0.25), 
         xlim=c(0,x_list), main=paste("lambda=", lambda_list[i]))
    x_seq<-seq(0,x_list,1)
    lines(x_seq, p_x, type="h", col="blue")
}