Left sum — Precalculus, what it means and where it is taught
Rectangles whose heights come from the left edge of each strip.
Taught in Precalculus.
Where it is taught
Practise this idea
2 questions in the course bank use Left sum, in Accumulation & Area Under a Curve.
Problem 1
For an increasing function, how does a left sum compare with the true area?
- Too small
- Too large
- Exactly right
- It depends on the width
Worked answer
Too small
Every rectangle stays under the curve
Problem 2
A left sum gives 12 and a right sum 18 for an increasing function. Give the midpoint of that bracket.
Worked answer
15
12+182 = 15