Math: Calculus
posted by REALLY NEED HELP!!!! .
Estimate the area under the graph of f(x)=x^2+2x from x = 4 to x = 10 using 3 approximating rectangles and left endpoints.
I got 290.25 as my answer but it's wrong. Would someone explain to me how to answer this question.

what is f(x) at x=4,6, 8
area=f(4)*2+f(6)*2 + f(8)*2
that is three rectangles of width 2, height to f(x)(left end point).
How in the world would you estimate to five digits of precision. "estimate"
f(4)=24
f(6)=48
f(8)=80
estimate: you do it. Twice the sum of those numbers.