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1、,Integrals,5,The Fundamental Theorem of Calculus,5.4,The Fundamental Theorem of Calculus,The Fundamental Theorem of Calculus is appropriately named because it establishes a connection between the two branches of calculus: differential calculus and integral calculus.It gives the precise inverse relat
2、ionship between the derivative and the integral.,The Fundamental Theorem of Calculus,The first part of the Fundamental Theorem deals with functions defined by an equation of the formwhere f is a continuous function on a, b and x varies between a and b. Observe that g depends only on x, which appears
3、 as the variable upper limit in the integral. If x is a fixed number, then the integral is a definite number.If we then let x vary, the number also varies and defines a function of x denoted by g(x).,The Fundamental Theorem of Calculus,If f happens to be a positive function, then g(x) can be interpr
4、eted as the area under the graph of f from a to x, where x can vary from a to b. (Think of g as the “area so far” function; see Figure 1.),Figure 1,Example 1 A Function Defined as an Integral,If f is the function whose graph is shown in Figure 2 and find the values of g(0), g(1), g(2), g(3), g(4), a
5、nd g(5). Then sketch a rough graph of g.,Figure 2,Example 1 Solution,First we notice that . From Figure 3(i) we see that g(1) is the area of a triangle:To find g(2) we again refer to Figure 3(ii) and add to g(1) the area of a rectangle:,Figure 3(i),Figure 3(ii),= (1 2) = 1,= 1 + (1 2) = 3,Example 1
6、Solution,We estimate that the area under f from 2 to 3 is about 1.3, soFor t 3, f (t) is negative and so we start subtracting areas:,contd,Figure 3(iii),Figure 3(iv), 3 + 1.3 = 4.3, 4.3 + (1.3) = 3.0,Example 1 Solution,We use these values to sketch the graph of g in Figure 4.Notice that, because f (
7、t) is positive for t 3, we keep adding area for t 3 and so g is increasing up to x = 3, where it attains a maximum value. For x 3, g decreases because f (t) is negative.,contd,Figure 3(v), 3 + (1.3) = 1.7,Figure 4,The Fundamental Theorem of Calculus,For the function, where a = 1 and f (t) = t2, noti
8、ce that g(x) = x2, that is, g = f. In other words, if g is defined as the integral of f by Equation 1, then g turns out to be an antiderivative of f, at least in this case. And if we sketch the derivative of the function g shown in Figure 4 by estimating slopes of tangents, we get a graph like that
9、of f in Figure 2. So we suspect that g = f in Example 1 too.,Figure 2,The Fundamental Theorem of Calculus,To see why this might be generally true we consider any continuous function f with f (x) 0. Then can be interpreted as the area under the graph of f from a to x, as in Figure 1.In order to compu
10、te g(x) from the definition of a derivative we first observe that, for h 0, g(x + h) g(x) is obtained by subtracting areas, so it is the area under the graph of f from x to x + h (the blue area in Figure 5).,Figure 1,Figure 5,The Fundamental Theorem of Calculus,For small h you can see from the figur
11、e that this area is approximately equal to the area of the rectangle with height f (x) and width h:g(x + h) g(x) hf (x)soIntuitively, we therefore expect that,The Fundamental Theorem of Calculus,The fact that this is true, even when f is not necessarily positive, is the first part of the Fundamental
12、 Theorem of Calculus.Using Leibniz notation for derivatives, we can write this theorem aswhen f is continuous.,The Fundamental Theorem of Calculus,Roughly speaking, this equation says that if we first integrate f and then differentiate the result, we get back to the original function f.It is easy to
13、 prove the Fundamental Theorem if we make the assumption that f possesses an antiderivative F. Then, by the Evaluation Theorem,for any x between a and b. Thereforeas required.,Example 3 Differentiating an Integral,Find the derivative of the functionSolution: Since is continuous, Part 1 of the Fundam
14、ental Theorem of Calculus gives,Example 4 A Function from Physics,Although a formula of the form may seem like a strange way of defining a function, books on physics, chemistry, and statistics are full of such functions. For instance, the Fresnel functionis named after the French physicist Augustin
15、Fresnel (17881827), who is famous for his works in optics.This function first appeared in Fresnels theory of the diffraction of light waves, but more recently it has been applied to the design of highways.,Example 4 A Function from Physics,Part 1 of the Fundamental Theorem tells us how to differenti
16、ate the Fresnel function:This means that we can apply all the methods of differential calculus to analyze S.Figure 6 shows the graphs of f (x) = sin(x2/2) and the Fresnel function,contd,Figure 6,Example 4 A Function from Physics,A computer was used to graph S by computing the value of this integral for many values of x.It does indeed look as if S(x) is the area under the graph of f from 0 to x until x 1.4 when S(x) becomes a difference of areas. Figure 7 shows a larger part of the graph of S.,
