Recap Video
Take a look at the following video which recaps the ideas from the section.
Example Video
Below is a video showing a worked example.
Problems
- Calculate and . We need to do base times height and add up the areas. Notice that since we are using rectangles, our base isFor the heights, we can plug in the left endpoint of our broken intervals into . Our two intervals are and , so the heights are and . Therefore, the approximationFor , our heights are given by the function at the right endpoints, so and . Therefore,
- Calculate and . We need to repeat the previous part’s steps, only with four rectangles instead of . Now, the base has length . The heights for , in increasing order of values, areThis gives us an approximation of . Similarly, for , the heights, in increasing order of -values, areThis gives us an approximation of .
- Calculate in terms of . You may find the identity
useful.We proceed as before. If we use rectangles, the length of the base will be (it’s ok to have things in terms of ). Now the heights. The first subinterval is , which means the first height isThe second subinterval will be , so the second height isSimilarly the third height will be . We will continue until the last height, which is . However, it will be useful to recognize that the last height comes from starting at and moving over ’s, i.e. writing the last height aswhich would simplify to . The reason for writing it in this form will be apparent in a moment. Now, we get thatHow can we simplify this? Let’s simplify the inside of the brackets by grouping the ’s and the rest. How many ’s are there? . Therefore, adding all the ’s gives , and the sum above simplifies toOut of the remaining terms, we can factor out a , i.e.Now, using the formula provided above, we get that this sum is equal toThis is the formula for .
- Use the previous part to find the area under on .
- The approximation , and .
- Based on the graph of , we see that will be an approximation for the area and will be anapproximation for the area.
- If is any number , then (in terms of )
- The smallest so that is .
- Use the identity to find an expression for in terms of . We
get
- The area under the curve on is , which in this case turns out to be .