Logarithmic differentials Let f be a differentiable function of one or more variables that is positive on its domain. a. Show that d ( ln f ) = d f f . b. Use part (a) to explain the statement that the absolute change in ln f is approximately equal to the relative change in f . c. Let f ( x, y ) = xy , note that ln f = ln x + ln y , and show that relative changes add: that is, df/f = dx/x + dy/y. d. Let f ( x, y ) = x/ y , note that ln f = ln x = ln y , and show that relative changes subtract; that is df /f = dx / x – dy / y. e. Show that in a product of n numbers, f = x 1 x 2 … x n , the relative change in f is approximately equal to the sum of the relative changes in the variables.
Logarithmic differentials Let f be a differentiable function of one or more variables that is positive on its domain. a. Show that d ( ln f ) = d f f . b. Use part (a) to explain the statement that the absolute change in ln f is approximately equal to the relative change in f . c. Let f ( x, y ) = xy , note that ln f = ln x + ln y , and show that relative changes add: that is, df/f = dx/x + dy/y. d. Let f ( x, y ) = x/ y , note that ln f = ln x = ln y , and show that relative changes subtract; that is df /f = dx / x – dy / y. e. Show that in a product of n numbers, f = x 1 x 2 … x n , the relative change in f is approximately equal to the sum of the relative changes in the variables.
Solution Summary: The author explains the differential equation d(mathrmlnf)=df
Logarithmic differentials Let f be a differentiable function of one or more variables that is positive on its domain.
a. Show that
d
(
ln
f
)
=
d
f
f
.
b. Use part (a) to explain the statement that the absolute change in ln f is approximately equal to the relative change in f.
c. Let f(x, y) = xy, note that ln f = ln x + ln y, and show that relative changes add: that is, df/f = dx/x + dy/y.
d. Let f(x, y) = x/y, note that ln f = ln x = ln y, and show that relative changes subtract; that is df /f = dx/x – dy/y.
e. Show that in a product of n numbers, f = x1x2…xn, the relative change in f is approximately equal to the sum of the relative changes in the variables.
Use the properties of logarithms, given that In(2) = 0.6931 and In(3) = 1.0986, to approximate the logarithm. Use a calculator to confirm your approximations. (Round your answers to four decimal places.)
(a) In(0.75)
(b) In(24)
(c) In(18)
1
(d) In
≈
2
72
Find the indefinite integral. (Remember the constant of integration.)
√tan(8x)
tan(8x) sec²(8x) dx
Chapter 15 Solutions
Calculus: Early Transcendentals, Books A La Carte Edition (3rd Edition)
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