### Home > CALC > Chapter 3 > Lesson 3.3.4 > Problem 3-136

3-136.

Write a Riemann sum to estimate *A*(*f*, 2 ≤ *x* ≤ 3) for *f*(*x*) = 9*x* − 2 with 20 left endpoint rectangles. Then compute the actual area geometrically and calculate the percent error. Homework Help ✎

APPROXIMATE AREA:

Left-endpoint Riemann sum:

Notice that there will be 20 rectangles squeezed into a 1 unit interval. This will be a very small Δ*x*, and a very good approximation of the area under the curve.

ACTUAL AREA: If you cannot visualize the familiar geometric shape that is formed when you graph *f*(*x*) = 9*x* − 2 on 2 ≤ *x* ≤ 3, then sketch a graph.