help("integrate")

# Create function
f<-function(x) x^3 + 2*x
  
# Integrate from 0 to 1
integrate(f, 0, 1)

1.25 with absolute error < 1.4e-14

# Create function
f <- function(x) {1/((x+1)*sqrt(x))}
  
# Integrate from 0 to 5
integrate(f, lower = 0, upper = 5)

2.300524 with absolute error < 0.00011