function f(x)
   return x - math.cos(x)
end

a = 0.0
b = 2.0
n = 10

h = ( b - a ) / n
sum1, sum2, sum3 = 0.0, 0.0, 0.0
x = a
for i = 1, n do
   sum1 = sum1 + f(x)
   x = x + h/2
   sum2 = sum2 + f(x)
   x = x + h/2
   sum3 = sum3 + f(x)
end
print( "Riemann sum using left endpoints: ", sum1 * h )
print( "Riemann sum using midpoints: ", sum2 * h )
print( "Riemann sum using right endpoints: ", sum3 * h )