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Derivative of ln⁡(x)cos⁡(x)\frac{\ln\left(x\right)}{\cos\left(x\right)}

The derivative of ln⁡(x)cos⁡(x)\frac{\ln\left(x\right)}{\cos\left(x\right)} is cos⁡(x)x−ln⁡(x)−sin⁡(x)cos⁡(x)2\frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}}.

f(x) =
ddx[ln⁡(x)cos⁡(x)]=cos⁡(x)x−ln⁡(x)−sin⁡(x)cos⁡(x)2\frac{d}{dx}\left[\frac{\ln\left(x\right)}{\cos\left(x\right)}\right] = \frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}}

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Graph of f(x) = ln(x) / cos(x) and its derivative-3-2-1123-10-5510152025slope 1.851f(x)f'(x)tangent at x = 1
Graph of f(x) = ln(x) / cos(x) and its derivative. The dashed line is the tangent at x = 1; its slope is f'(1) = 1.8508.

How to work it out

  1. 1

    We differentiate f(x)=ln⁡(x)cos⁡(x)f(x) = \frac{\ln\left(x\right)}{\cos\left(x\right)} with respect to x. The rule that applies is the quotient rule.

    f(x)=ln⁡(x)cos⁡(x)f(x) = \frac{\ln\left(x\right)}{\cos\left(x\right)}
  2. 2

    Quotient rule: (uv)′=u′v−uv′v2\left(\frac{u}{v}\right)' = \frac{u'v - uv'}{v^{2}}. Let u=ln⁡(x)u = \ln\left(x\right) and v=cos⁡(x)v = \cos\left(x\right).

    u=ln⁡(x),v=cos⁡(x)u = \ln\left(x\right),\quad v = \cos\left(x\right)
  3. 3

    Differentiate each piece:

    u′=1x,v′=−sin⁡(x)u' = \frac{1}{x},\quad v' = -\sin\left(x\right)
  4. 4

    Put them in the rule:

    f′(x)=(1x)(cos⁡(x))−(ln⁡(x))(−sin⁡(x))(cos⁡(x))2f'(x) = \frac{\left(\frac{1}{x}\right)\left(\cos\left(x\right)\right) - \left(\ln\left(x\right)\right)\left(-\sin\left(x\right)\right)}{\left(\cos\left(x\right)\right)^{2}}
  5. 5

    Simplify:

    f′(x)=cos⁡(x)x−ln⁡(x)−sin⁡(x)cos⁡(x)2f'(x) = \frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}}
  6. 6

    Differentiating once more gives the second derivative, which tells you about curvature:

    f′′(x)=(−(sin⁡(x)x)−cos⁡(x)x2−(−sin⁡(x)x+ln⁡(x)−cos⁡(x)))cos⁡(x)2−(cos⁡(x)x−ln⁡(x)−sin⁡(x))2cos⁡(x)−sin⁡(x)(cos⁡(x)2)2f''(x) = \frac{\left(\frac{-\left(\sin\left(x\right) x\right) - \cos\left(x\right)}{x^{2}} - \left(\frac{-\sin\left(x\right)}{x} + \ln\left(x\right) -\cos\left(x\right)\right)\right) \cos\left(x\right)^{2} - \left(\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)\right) 2 \cos\left(x\right) -\sin\left(x\right)}{\left(\cos\left(x\right)^{2}\right)^{2}}
LaTeX source of the formulas on this page
\[ \frac{d}{dx}\left[\frac{\ln\left(x\right)}{\cos\left(x\right)}\right] = \frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}} \]
\[ f(x) = \frac{\ln\left(x\right)}{\cos\left(x\right)} \]
\[ u = \ln\left(x\right),\quad v = \cos\left(x\right) \]
\[ u' = \frac{1}{x},\quad v' = -\sin\left(x\right) \]
\[ f'(x) = \frac{\left(\frac{1}{x}\right)\left(\cos\left(x\right)\right) - \left(\ln\left(x\right)\right)\left(-\sin\left(x\right)\right)}{\left(\cos\left(x\right)\right)^{2}} \]
\[ f'(x) = \frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}} \]
\[ f''(x) = \frac{\left(\frac{-\left(\sin\left(x\right) x\right) - \cos\left(x\right)}{x^{2}} - \left(\frac{-\sin\left(x\right)}{x} + \ln\left(x\right) -\cos\left(x\right)\right)\right) \cos\left(x\right)^{2} - \left(\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)\right) 2 \cos\left(x\right) -\sin\left(x\right)}{\left(\cos\left(x\right)^{2}\right)^{2}} \]

Values of f and f' for ln(x) / cos(x)

xf(x)f'(x)
0.5-0.7898371.8474979
101.8508157
2-1.66563132.4379717
3-1.1097178-0.17851645

Questions

What is the derivative of ln(x) / cos(x)?

The derivative of ln⁡(x)cos⁡(x)\frac{\ln\left(x\right)}{\cos\left(x\right)} is cos⁡(x)x−ln⁡(x)−sin⁡(x)cos⁡(x)2\frac{\frac{\cos\left(x\right)}{x} - \ln\left(x\right) -\sin\left(x\right)}{\cos\left(x\right)^{2}}.

What is the second derivative of ln(x) / cos(x)?

(((-(sin(x) * x) - cos(x)) / x2x^{2} - (-sin(x) / x + ln(x) * -cos(x))) * cos(x)^2 - (cos(x) / x - ln(x) * -sin(x)) * 2cos(x) * -sin(x)) / (cos(x)^2)^2.

Which rule do you use for ln(x) / cos(x)?

The quotient rule.

What is the slope of ln(x) / cos(x) at x = 1?

1.8508157.

Related derivatives

    Derivative of ln(x) / cos(x): (cos(x) / x - ln(x) * -sin(x)) / cos(x)^2 (with steps) | WordGPT