Estimate the area under the graph of f(x)=x2+4x from x=4 to x=12 using 4 approximating rectangles and left endpoints.
Approximation =
each interval has width (12-4)/4 = 2
so the area is approximated by
2(f(4)+f(6)+f(8)+f(10))
so do the math and let 'er rip
Hoping you made your sketch
area = appr (( f(4) + f(6) + f(8) + f(10)) * 2
= 2(32 + 60 + 96 + 140)
= 656