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MATH 140 (141)
Ewa Duma (13)
Lecture 13

Lecture 13 - 3.1.pdf

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Department
Mathematics & Statistics (Sci)
Course
MATH 140
Professor
Ewa Duma
Semester
Summer

Description
f▯x ▯ h▯ ▯ f▯x▯ c ▯ c f▯▯x▯ ▯ lim ▯ lim ▯ lim 0 ▯ 0 hl0 h hl0 h hl0 0 x In Leibniz notation, we write this rule as follows. FIGURE 1 The graph of ƒ=c is the line y=c, so fª(x)=0. DERIVATIVE OF A CONSTANT FUNCTION MATH140 - Lecture 13 Notes d ▯c▯ ▯ 0 dx Derivatives of Polynomials and Exponential Functions: Derivative of a constant function: d/dx (c) = 0 POWER FUNCTIONS y n We next look at the functions f▯x▯ ▯ x , where n is a positive integer. If n ▯ 1, the graph of f▯x▯ ▯ x is the line y ▯ x, which has slope 1. (See Figure 2.) So y=x 1766 |||||CHAPTER 3 DIFFERENTIATION RULESS Power Functions: slope=1 d 1 V EXAMPLE 3 Find equations dx the tangent line and normal line to the curve y ▯sx x V EXAMPLE 3 For functions f(x) = x^n, where n is a positive integer. If n = 1, the graph of f(x) = x is the 0 at the point ▯1, 1▯. Illustrate by graphing the curve and these lines. x line y = x, which has a slope1▯2 1. 3▯2refore, the derivative of x is equal to 1. (You canSOLUTION The derivative of f▯x▯ ▯sxx ▯ xxn of ▯ xeriistive.) We have already FIGURE 2 investigated the casesExamples:d n ▯ 3. In 3ac▯3▯2▯▯1e3ti1▯22.3 (Exercises 17 and 18) we The graph of ƒ=x 3s the found that f▯▯x▯ ▯ 2x ▯ x2 ▯▯ 2ssxx line y=x, so fª(x)=1. d d 3 tangent 2 So the slope of the▯x ▯ ▯ 2xline at (1, ▯x ▯ ▯ 3x2▯ ▯ . Therefore an equation of the tan- 6 030102 tangent gent line is dx dx 3 33 11 y ▯ 1 ▯ ▯2 ▯ 1▯ orr y ▯ 22▯ 22 normall For n ▯ 4 we find the derivative of f▯x▯ ▯ x as follows: The normal line is perpendicular to the tangent line, so its slope is the negative recipro-er, then we call _1 3 The no3mal line i22perpendicular to the tangent line, so its slope is the negative recipro- _1 3 cal of2, that is,33 Thf▯x ▯ h▯ ▯ f▯x▯of the no▯x ▯ h▯ ▯ xs 4 f▯▯x▯ ▯ lim ▯ lim hl0y ▯ 1 ▯ ▯ ▯x ▯ 1▯ hl0orr y ▯ ▯ x ▯ 5 _1 The evide4ce lie3 in the2 2llowing3formu4a: 4 3 x ▯ 4x h ▯ 6x h ▯ 4xh ▯ h ▯ x FIGURE 44 We graph the curvehl0d its tangent line hnd normal line in Figure 4. MM X^n - a^n = (x-a)(x^(n-1)+x^(n-2)a + … + xa^(n-2) + a^(n-1)) 3 2 2 3 4 NEW DERIVATIVES▯ lim OLD h ▯ 6x h ▯ 4xh ▯ h hl0 h When new functions are formed from old functions by addition, subtraction, or multipli- ▯ lim ▯4x ▯ 6x h ▯ 4xh ▯ h ▯ ▯ 4x 3 cation by a constahl0 their derivatives can be calculated in terms of derivatives of the old functions. In particular, the following formula says that the derivative of a constant timesn is the Thus a function is constant times the derivative of the function.ion. 3 d ▯x ▯ ▯ 4x 3 NNGGEOMETRIC INTERPRETATION OF dx TTHE CONSTANT MULTIPLE RULE THE CONSTANDefinition: The constant multiple rule says that if c is a constant and f is a differentiable tion, then function, then: y dd d 173 yy=2ƒ ▯cf▯x▯▯ ▯ c f▯x▯ dx ddx d/dx [cf(x)] = c(d/dx)⋅f(x) yy=ƒ Assuming that g(x) = cf(x), we can show the following: PROOF LLet t▯x▯ ▯ cf▯x▯. Then 00 x t▯x ▯ h▯ ▯ t▯x▯ cf▯x ▯ h▯ ▯ cf▯x▯ t▯▯x▯ ▯ lim ▯▯ lim MMultiplying by c ▯ 2 stretches the graph verti- hhl00 h hhl00 h ccally by a factor of 2. All the rises have been doubled but the runs stay the same. So the f▯x ▯ h▯ ▯ f▯x▯
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