# 第3题
a=1
b=2
c=(-log(a)+sqrt(b*b-4*a))/(a*2)
print(c)
#第4题
now<-2010
year<-c(1990,1970,1972,1982,1983)
mean_age<-mean(now-year)
mean_age_sd<-sd(mean_age)
max_min<-max(now-year)-min(now-year)
