Presentation on theme: "Chapter 5 Integrals 5.1 Areas and Distances"— Presentation transcript:
1Chapter 5 Integrals 5.1 Areas and Distances In this handout:The Area problemArea under a ParabolaDefinition of the AreaThe Distance problem
2The Area Problem1y=x2Consider the problem of determining the area of the domain bounded by the graph of the function x2, the x-axis, and the lines x=0 and x=1.We determine the area by approximating the domain with thin rectangles for which the area can be directly computed. Letting these rectangles get thinner, the approximation gets better and, at the limit, we get the area of the domain in question.As the number n of the approximating rectangles grows, the approximation gets better.
3Height of the kth rectangle. Length of the bottom.Let A denote the actual area of the domain in question. Clearly sn<A for all n.Lower est. snUpper est. Sn
4This can be computed directly using a previously derived formula for the sum of squares. Solution follows.
5y=x21ConcludeThe blue area under the curve y=x2 over the interval [0,1] equals 1/3.
6Definition of AreaGeneralizing from the previous example, we have the following definition.The area A of the region S under the graph of the continuous function f is the limit of the sum of the areas of approximating rectangles:Note that instead of using left endpoints or right endpoints, we could take the height of the ith rectangle to be the value of f at any number xi* in the subinterval [xi-1, xi].That number is called a sample point.
7The Distance ProblemConsider an object moving at a constant rate of 3 ft/sec.Since rate . time = distance: 3t = dIf we draw a graph of the velocity, the distance that the object travels is equal to the area under the line.timevelocityAfter 4 seconds, the object has gone 12 feet.
8If the velocity is not constant, we might guess that thedistance traveled is still equalto the area under the curve.Example:We could estimate the area under the curve by drawing rectangles touching at their left corners.Approximate area:
9We could also estimate the area under the curve by drawing rectangles touching at their right corners.Approximate area:
10Another approach would be to use rectangles that touch at the midpoint. In this example there are four subintervals.As the number of subintervals increases, so does the accuracy.Approximate area:
11The exact answer for this problem is . With 8 subintervals:Approximate area:The exact answer for thisproblem iswidth of subinterval
12Measuring the distance In general, suppose an object moves with velocity v=f(t), where a ≤ t ≤ b and f(t)≥0.Take velocity readings at times t0 (=a), t1 , …, tn (=b) so that the velocity is approximately constant on each subinterval.The time between consecutive readings is Δt = (b-a)/n.Then the exact distance d traveled is