
Katelyn S. answered 04/01/19
Experienced Math Tutor
To find the integral is the same as finding the area under the curve of a line.To find the integral using left sum, construct the rectangles that have a height at the left endpoint, calculate their areas, and add them up. Since the x values do not have a consistent difference (some values are 2 apart, some are 1 apart), you won't have a constant value for delta x. This means you will have to find the areas of 6 rectangles with different bases.
The first rectangle has a height of 4 (the f(1)=4) and a width of 2 (3-1=2), so the area is 6. The next rectangle has a height of 8 (f(3)=8) and a width of 1 (4-1=8), so the area is 8. Following this logic, you find the areas to be 6, 8, 12, 10, 20, and 14. Adding those up, the integral is 70.
Hope that helped!