For the function f(x)=10-4(x^2), find a formula for the lower sum obtained by dividing the interval [0,1] into n equal subintervals. Then take the limit as n-infinity to calculate the area under the curve over [0,1].

Question

For the function f(x)=10-4(x^2), find a formula for the lower sum obtained by dividing the interval [0,1] into n equal subintervals. Then take the limit as n->infinity to calculate the area under the curve over [0,1].

I only need help with the first part. I don't really understand how to find the formula for the lower sum.  
i wrote down in my notes that a=w*h
w= (upper limit-lower limit)/n
h= (i*w)^2
and a= h[(n(n+1)(2n+1))/6]
but I don't really understand what "i" stands for, so I don't know how to use the formula.

Daniel · Answer

YA i can't fingure out how to use it either im thinking that it could be the xi = a+x(change of x)