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Derivative of x3cos⁡(x)\frac{x^{3}}{\cos\left(x\right)}

The derivative of x3cos⁡(x)\frac{x^{3}}{\cos\left(x\right)} is 3x2cos⁡(x)−x3−sin⁡(x)cos⁡(x)2\frac{3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)}{\cos\left(x\right)^{2}}.

f(x) =
ddx[x3cos⁡(x)]=3x2cos⁡(x)−x3−sin⁡(x)cos⁡(x)2\frac{d}{dx}\left[\frac{x^{3}}{\cos\left(x\right)}\right] = \frac{3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)}{\cos\left(x\right)^{2}}

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Graph of f(x) = x^3 / cos(x) and its derivative-3-2-1123-5050100150200250slope 8.435f(x)f'(x)tangent at x = 1
Graph of f(x) = x^3 / cos(x) and its derivative. The dashed line is the tangent at x = 1; its slope is f'(1) = 8.4349.

How to work it out

  1. 1

    We differentiate f(x)=x3cos⁡(x)f(x) = \frac{x^{3}}{\cos\left(x\right)} with respect to x. The rule that applies is the quotient rule.

    f(x)=x3cos⁡(x)f(x) = \frac{x^{3}}{\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=x3u = x^{3} and v=cos⁡(x)v = \cos\left(x\right).

    u=x3,v=cos⁡(x)u = x^{3},\quad v = \cos\left(x\right)
  3. 3

    Differentiate each piece:

    u′=3x2,v′=−sin⁡(x)u' = 3 x^{2},\quad v' = -\sin\left(x\right)
  4. 4

    Put them in the rule:

    f′(x)=(3x2)(cos⁡(x))−(x3)(−sin⁡(x))(cos⁡(x))2f'(x) = \frac{\left(3 x^{2}\right)\left(\cos\left(x\right)\right) - \left(x^{3}\right)\left(-\sin\left(x\right)\right)}{\left(\cos\left(x\right)\right)^{2}}
  5. 5

    Simplify:

    f′(x)=3x2cos⁡(x)−x3−sin⁡(x)cos⁡(x)2f'(x) = \frac{3 x^{2} \cos\left(x\right) - x^{3} -\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)=(6xcos⁡(x)+3x2−sin⁡(x)−(3x2−sin⁡(x)+x3−cos⁡(x)))cos⁡(x)2−(3x2cos⁡(x)−x3−sin⁡(x))2cos⁡(x)−sin⁡(x)(cos⁡(x)2)2f''(x) = \frac{\left(6 x \cos\left(x\right) + 3 x^{2} -\sin\left(x\right) - \left(3 x^{2} -\sin\left(x\right) + x^{3} -\cos\left(x\right)\right)\right) \cos\left(x\right)^{2} - \left(3 x^{2} \cos\left(x\right) - x^{3} -\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
\[ \frac{d}{dx}\left[\frac{x^{3}}{\cos\left(x\right)}\right] = \frac{3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)}{\cos\left(x\right)^{2}} \]
\[ f(x) = \frac{x^{3}}{\cos\left(x\right)} \]
\[ u = x^{3},\quad v = \cos\left(x\right) \]
\[ u' = 3 x^{2},\quad v' = -\sin\left(x\right) \]
\[ f'(x) = \frac{\left(3 x^{2}\right)\left(\cos\left(x\right)\right) - \left(x^{3}\right)\left(-\sin\left(x\right)\right)}{\left(\cos\left(x\right)\right)^{2}} \]
\[ f'(x) = \frac{3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)}{\cos\left(x\right)^{2}} \]
\[ f''(x) = \frac{\left(6 x \cos\left(x\right) + 3 x^{2} -\sin\left(x\right) - \left(3 x^{2} -\sin\left(x\right) + x^{3} -\cos\left(x\right)\right)\right) \cos\left(x\right)^{2} - \left(3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)\right) 2 \cos\left(x\right) -\sin\left(x\right)}{\left(\cos\left(x\right)^{2}\right)^{2}} \]

Values of f and f' for x3x^{3} / cos(x)

xf(x)f'(x)
-219.22398413.169195
-1-1.85081578.4349218
0.50.142436740.93243399
11.85081578.4349218
2-19.22398413.169195
3-27.272934-23.385272

Questions

What is the derivative of x3x^{3} / cos(x)?

The derivative of x3cos⁡(x)\frac{x^{3}}{\cos\left(x\right)} is 3x2cos⁡(x)−x3−sin⁡(x)cos⁡(x)2\frac{3 x^{2} \cos\left(x\right) - x^{3} -\sin\left(x\right)}{\cos\left(x\right)^{2}}.

What is the second derivative of x3x^{3} / cos(x)?

((6x * cos(x) + 3 * x2x^{2} * -sin(x) - (3 * x2x^{2} * -sin(x) + x3x^{3} * -cos(x))) * cos(x)^2 - (3 * x2x^{2} * cos(x) - x3x^{3} * -sin(x)) * 2cos(x) * -sin(x)) / (cos(x)^2)^2.

Which rule do you use for x3x^{3} / cos(x)?

The quotient rule.

What is the slope of x3x^{3} / cos(x) at x = 1?

8.4349218.

Related derivatives

    Derivative of x^3 / cos(x): (3 * x^2 * cos(x) - x^3 * -sin(x)) / cos(x)^2 (with steps) | WordGPT