Estimate the area under the graph of f(x) =x^2 + 4x from x=1 to x=9

[ProBasket]

Estimate the area under the graph of f(x) =x^2 + 4x from x=1 to x=9 using 4 approximating rectangles and left endpoints.

first i had to find delta x, so i did 9-1/4 = 2
which means x0 = 0, x1 = 2, x2= 4, x3=6 (since I'm using left endpoints, i include x0)

after that, i just plug it in the left end point formula:
L4 = 2*0 + 2*12 + 2*32 + 2*60 = 208

i done the calculations many time and get the same answer, am i missing something?

 

[vincentchan]

the x's should be 1,3,5,7... you started at 1

 

[ProBasket]

ah, i see. thanks for the help.