Mister Exam

Derivative of (sinx+cosx)(tanx+cotx)

Function f() - derivative -N order at the point
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(sin(x) + cos(x))*(tan(x) + cot(x))
(sin(x)+cos(x))(tan(x)+cot(x))\left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right)
d                                      
--((sin(x) + cos(x))*(tan(x) + cot(x)))
dx                                     
ddx(sin(x)+cos(x))(tan(x)+cot(x))\frac{d}{d x} \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right)
Detail solution
  1. Apply the product rule:

    ddxf(x)g(x)=f(x)ddxg(x)+g(x)ddxf(x)\frac{d}{d x} f{\left(x \right)} g{\left(x \right)} = f{\left(x \right)} \frac{d}{d x} g{\left(x \right)} + g{\left(x \right)} \frac{d}{d x} f{\left(x \right)}

    f(x)=sin(x)+cos(x)f{\left(x \right)} = \sin{\left(x \right)} + \cos{\left(x \right)}; to find ddxf(x)\frac{d}{d x} f{\left(x \right)}:

    1. Differentiate sin(x)+cos(x)\sin{\left(x \right)} + \cos{\left(x \right)} term by term:

      1. The derivative of sine is cosine:

        ddxsin(x)=cos(x)\frac{d}{d x} \sin{\left(x \right)} = \cos{\left(x \right)}

      2. The derivative of cosine is negative sine:

        ddxcos(x)=sin(x)\frac{d}{d x} \cos{\left(x \right)} = - \sin{\left(x \right)}

      The result is: sin(x)+cos(x)- \sin{\left(x \right)} + \cos{\left(x \right)}

    g(x)=tan(x)+cot(x)g{\left(x \right)} = \tan{\left(x \right)} + \cot{\left(x \right)}; to find ddxg(x)\frac{d}{d x} g{\left(x \right)}:

    1. Differentiate tan(x)+cot(x)\tan{\left(x \right)} + \cot{\left(x \right)} term by term:

      1. Rewrite the function to be differentiated:

        tan(x)=sin(x)cos(x)\tan{\left(x \right)} = \frac{\sin{\left(x \right)}}{\cos{\left(x \right)}}

      2. Apply the quotient rule, which is:

        ddxf(x)g(x)=f(x)ddxg(x)+g(x)ddxf(x)g2(x)\frac{d}{d x} \frac{f{\left(x \right)}}{g{\left(x \right)}} = \frac{- f{\left(x \right)} \frac{d}{d x} g{\left(x \right)} + g{\left(x \right)} \frac{d}{d x} f{\left(x \right)}}{g^{2}{\left(x \right)}}

        f(x)=sin(x)f{\left(x \right)} = \sin{\left(x \right)} and g(x)=cos(x)g{\left(x \right)} = \cos{\left(x \right)}.

        To find ddxf(x)\frac{d}{d x} f{\left(x \right)}:

        1. The derivative of sine is cosine:

          ddxsin(x)=cos(x)\frac{d}{d x} \sin{\left(x \right)} = \cos{\left(x \right)}

        To find ddxg(x)\frac{d}{d x} g{\left(x \right)}:

        1. The derivative of cosine is negative sine:

          ddxcos(x)=sin(x)\frac{d}{d x} \cos{\left(x \right)} = - \sin{\left(x \right)}

        Now plug in to the quotient rule:

        sin2(x)+cos2(x)cos2(x)\frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)}}

      3. There are multiple ways to do this derivative.

        Method #1

        1. Rewrite the function to be differentiated:

          cot(x)=1tan(x)\cot{\left(x \right)} = \frac{1}{\tan{\left(x \right)}}

        2. Let u=tan(x)u = \tan{\left(x \right)}.

        3. Apply the power rule: 1u\frac{1}{u} goes to 1u2- \frac{1}{u^{2}}

        4. Then, apply the chain rule. Multiply by ddxtan(x)\frac{d}{d x} \tan{\left(x \right)}:

          1. ddxtan(x)=1cos2(x)\frac{d}{d x} \tan{\left(x \right)} = \frac{1}{\cos^{2}{\left(x \right)}}

          The result of the chain rule is:

          sin2(x)+cos2(x)cos2(x)tan2(x)- \frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)} \tan^{2}{\left(x \right)}}

        Method #2

        1. Rewrite the function to be differentiated:

          cot(x)=cos(x)sin(x)\cot{\left(x \right)} = \frac{\cos{\left(x \right)}}{\sin{\left(x \right)}}

        2. Apply the quotient rule, which is:

          ddxf(x)g(x)=f(x)ddxg(x)+g(x)ddxf(x)g2(x)\frac{d}{d x} \frac{f{\left(x \right)}}{g{\left(x \right)}} = \frac{- f{\left(x \right)} \frac{d}{d x} g{\left(x \right)} + g{\left(x \right)} \frac{d}{d x} f{\left(x \right)}}{g^{2}{\left(x \right)}}

          f(x)=cos(x)f{\left(x \right)} = \cos{\left(x \right)} and g(x)=sin(x)g{\left(x \right)} = \sin{\left(x \right)}.

          To find ddxf(x)\frac{d}{d x} f{\left(x \right)}:

          1. The derivative of cosine is negative sine:

            ddxcos(x)=sin(x)\frac{d}{d x} \cos{\left(x \right)} = - \sin{\left(x \right)}

          To find ddxg(x)\frac{d}{d x} g{\left(x \right)}:

          1. The derivative of sine is cosine:

            ddxsin(x)=cos(x)\frac{d}{d x} \sin{\left(x \right)} = \cos{\left(x \right)}

          Now plug in to the quotient rule:

          sin2(x)cos2(x)sin2(x)\frac{- \sin^{2}{\left(x \right)} - \cos^{2}{\left(x \right)}}{\sin^{2}{\left(x \right)}}

      The result is: sin2(x)+cos2(x)cos2(x)sin2(x)+cos2(x)cos2(x)tan2(x)\frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)}} - \frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)} \tan^{2}{\left(x \right)}}

    The result is: (sin2(x)+cos2(x)cos2(x)sin2(x)+cos2(x)cos2(x)tan2(x))(sin(x)+cos(x))+(sin(x)+cos(x))(tan(x)+cot(x))\left(\frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)}} - \frac{\sin^{2}{\left(x \right)} + \cos^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)} \tan^{2}{\left(x \right)}}\right) \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) + \left(- \sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right)

  2. Now simplify:

    1cos(x)+1sin(x)+4sin(x)cos(2x)+182sin(x+π4)1cos(4x)\frac{1}{\cos{\left(x \right)}} + \frac{1}{\sin{\left(x \right)}} + \frac{4 \sin{\left(x \right)}}{\cos{\left(2 x \right)} + 1} - \frac{8 \sqrt{2} \sin{\left(x + \frac{\pi}{4} \right)}}{1 - \cos{\left(4 x \right)}}


The answer is:

1cos(x)+1sin(x)+4sin(x)cos(2x)+182sin(x+π4)1cos(4x)\frac{1}{\cos{\left(x \right)}} + \frac{1}{\sin{\left(x \right)}} + \frac{4 \sin{\left(x \right)}}{\cos{\left(2 x \right)} + 1} - \frac{8 \sqrt{2} \sin{\left(x + \frac{\pi}{4} \right)}}{1 - \cos{\left(4 x \right)}}

The graph
02468-8-6-4-2-1010-1000010000
The first derivative [src]
/   2         2   \                                                         
\tan (x) - cot (x)/*(sin(x) + cos(x)) + (-sin(x) + cos(x))*(tan(x) + cot(x))
(sin(x)+cos(x))(tan(x)+cot(x))+(sin(x)+cos(x))(tan2(x)cot2(x))\left(- \sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right) + \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan^{2}{\left(x \right)} - \cot^{2}{\left(x \right)}\right)
The second derivative [src]
                                         /   2         2   \                        //       2   \          /       2   \       \                  
-(cos(x) + sin(x))*(cot(x) + tan(x)) - 2*\tan (x) - cot (x)/*(-cos(x) + sin(x)) + 2*\\1 + cot (x)/*cot(x) + \1 + tan (x)/*tan(x)/*(cos(x) + sin(x))
2((tan2(x)+1)tan(x)+(cot2(x)+1)cot(x))(sin(x)+cos(x))2(sin(x)cos(x))(tan2(x)cot2(x))(sin(x)+cos(x))(tan(x)+cot(x))2 \left(\left(\tan^{2}{\left(x \right)} + 1\right) \tan{\left(x \right)} + \left(\cot^{2}{\left(x \right)} + 1\right) \cot{\left(x \right)}\right) \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) - 2 \left(\sin{\left(x \right)} - \cos{\left(x \right)}\right) \left(\tan^{2}{\left(x \right)} - \cot^{2}{\left(x \right)}\right) - \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right)
The third derivative [src]
                                                                                                                                                                          /             2                2                                                    \
                                                            //       2   \          /       2   \       \     /   2         2   \                                         |/       2   \    /       2   \         2    /       2   \        2    /       2   \|
(-cos(x) + sin(x))*(cot(x) + tan(x)) - 6*(-cos(x) + sin(x))*\\1 + cot (x)/*cot(x) + \1 + tan (x)/*tan(x)/ - 3*\tan (x) - cot (x)/*(cos(x) + sin(x)) + 2*(cos(x) + sin(x))*\\1 + tan (x)/  - \1 + cot (x)/  - 2*cot (x)*\1 + cot (x)/ + 2*tan (x)*\1 + tan (x)//
6((tan2(x)+1)tan(x)+(cot2(x)+1)cot(x))(sin(x)cos(x))+(sin(x)cos(x))(tan(x)+cot(x))3(sin(x)+cos(x))(tan2(x)cot2(x))+2(sin(x)+cos(x))((tan2(x)+1)2+2(tan2(x)+1)tan2(x)(cot2(x)+1)22(cot2(x)+1)cot2(x))- 6 \left(\left(\tan^{2}{\left(x \right)} + 1\right) \tan{\left(x \right)} + \left(\cot^{2}{\left(x \right)} + 1\right) \cot{\left(x \right)}\right) \left(\sin{\left(x \right)} - \cos{\left(x \right)}\right) + \left(\sin{\left(x \right)} - \cos{\left(x \right)}\right) \left(\tan{\left(x \right)} + \cot{\left(x \right)}\right) - 3 \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\tan^{2}{\left(x \right)} - \cot^{2}{\left(x \right)}\right) + 2 \left(\sin{\left(x \right)} + \cos{\left(x \right)}\right) \left(\left(\tan^{2}{\left(x \right)} + 1\right)^{2} + 2 \left(\tan^{2}{\left(x \right)} + 1\right) \tan^{2}{\left(x \right)} - \left(\cot^{2}{\left(x \right)} + 1\right)^{2} - 2 \left(\cot^{2}{\left(x \right)} + 1\right) \cot^{2}{\left(x \right)}\right)
The graph
Derivative of (sinx+cosx)(tanx+cotx)