Derivative of y=sin(2x)*cot(x*pi/4)

1. Apply the product rule:

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

   $f{\left(x \right)} = \sin{\left(2 x \right)}$; to find $\frac{d}{d x} f{\left(x \right)}$:

   1. Let $u = 2 x$.

   2. The derivative of sine is cosine:

      $$\frac{d}{d u} \sin{\left(u \right)} = \cos{\left(u \right)}$$

   3. Then, apply the chain rule. Multiply by $\frac{d}{d x} 2 x$:

      1. The derivative of a constant times a function is the constant times the derivative of the function.

         1. Apply the power rule: $x$ goes to $1$

         So, the result is: $2$

      The result of the chain rule is:

      $$2 \cos{\left(2 x \right)}$$

   $g{\left(x \right)} = \cot{\left(\frac{\pi x}{4} \right)}$; to find $\frac{d}{d x} g{\left(x \right)}$:

   1. There are multiple ways to do this derivative.

      Method #1

      1. Rewrite the function to be differentiated:

         $$\cot{\left(\frac{\pi x}{4} \right)} = \frac{1}{\tan{\left(\frac{\pi x}{4} \right)}}$$

      2. Let $u = \tan{\left(\frac{\pi x}{4} \right)}$.

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

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

         1. Rewrite the function to be differentiated:

            $$\tan{\left(\frac{\pi x}{4} \right)} = \frac{\sin{\left(\frac{\pi x}{4} \right)}}{\cos{\left(\frac{\pi x}{4} \right)}}$$

         2. Apply the quotient rule, which is:

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

            $f{\left(x \right)} = \sin{\left(\frac{\pi x}{4} \right)}$ and $g{\left(x \right)} = \cos{\left(\frac{\pi x}{4} \right)}$.

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

            1. Let $u = \frac{\pi x}{4}$.

            2. The derivative of sine is cosine:

               $$\frac{d}{d u} \sin{\left(u \right)} = \cos{\left(u \right)}$$

            3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \frac{\pi x}{4}$:

               1. The derivative of a constant times a function is the constant times the derivative of the function.

                  1. The derivative of a constant times a function is the constant times the derivative of the function.

                     1. Apply the power rule: $x$ goes to $1$

                     So, the result is: $\pi$

                  So, the result is: $\frac{\pi}{4}$

               The result of the chain rule is:

               $$\frac{\pi \cos{\left(\frac{\pi x}{4} \right)}}{4}$$

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

            1. Let $u = \frac{\pi x}{4}$.

            2. The derivative of cosine is negative sine:

               $$\frac{d}{d u} \cos{\left(u \right)} = - \sin{\left(u \right)}$$

            3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \frac{\pi x}{4}$:

               1. The derivative of a constant times a function is the constant times the derivative of the function.

                  1. The derivative of a constant times a function is the constant times the derivative of the function.

                     1. Apply the power rule: $x$ goes to $1$

                     So, the result is: $\pi$

                  So, the result is: $\frac{\pi}{4}$

               The result of the chain rule is:

               $$- \frac{\pi \sin{\left(\frac{\pi x}{4} \right)}}{4}$$

            Now plug in to the quotient rule:

            $\frac{\frac{\pi \sin^{2}{\left(\frac{\pi x}{4} \right)}}{4} + \frac{\pi \cos^{2}{\left(\frac{\pi x}{4} \right)}}{4}}{\cos^{2}{\left(\frac{\pi x}{4} \right)}}$

         The result of the chain rule is:

         $$- \frac{\frac{\pi \sin^{2}{\left(\frac{\pi x}{4} \right)}}{4} + \frac{\pi \cos^{2}{\left(\frac{\pi x}{4} \right)}}{4}}{\cos^{2}{\left(\frac{\pi x}{4} \right)} \tan^{2}{\left(\frac{\pi x}{4} \right)}}$$

      Method #2

      1. Rewrite the function to be differentiated:

         $$\cot{\left(\frac{\pi x}{4} \right)} = \frac{\cos{\left(\frac{\pi x}{4} \right)}}{\sin{\left(\frac{\pi x}{4} \right)}}$$

      2. Apply the quotient rule, which is:

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

         $f{\left(x \right)} = \cos{\left(\frac{\pi x}{4} \right)}$ and $g{\left(x \right)} = \sin{\left(\frac{\pi x}{4} \right)}$.

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

         1. Let $u = \frac{\pi x}{4}$.

         2. The derivative of cosine is negative sine:

            $$\frac{d}{d u} \cos{\left(u \right)} = - \sin{\left(u \right)}$$

         3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \frac{\pi x}{4}$:

            1. The derivative of a constant times a function is the constant times the derivative of the function.

               1. The derivative of a constant times a function is the constant times the derivative of the function.

                  1. Apply the power rule: $x$ goes to $1$

                  So, the result is: $\pi$

               So, the result is: $\frac{\pi}{4}$

            The result of the chain rule is:

            $$- \frac{\pi \sin{\left(\frac{\pi x}{4} \right)}}{4}$$

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

         1. Let $u = \frac{\pi x}{4}$.

         2. The derivative of sine is cosine:

            $$\frac{d}{d u} \sin{\left(u \right)} = \cos{\left(u \right)}$$

         3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \frac{\pi x}{4}$:

            1. The derivative of a constant times a function is the constant times the derivative of the function.

               1. The derivative of a constant times a function is the constant times the derivative of the function.

                  1. Apply the power rule: $x$ goes to $1$

                  So, the result is: $\pi$

               So, the result is: $\frac{\pi}{4}$

            The result of the chain rule is:

            $$\frac{\pi \cos{\left(\frac{\pi x}{4} \right)}}{4}$$

         Now plug in to the quotient rule:

         $\frac{- \frac{\pi \sin^{2}{\left(\frac{\pi x}{4} \right)}}{4} - \frac{\pi \cos^{2}{\left(\frac{\pi x}{4} \right)}}{4}}{\sin^{2}{\left(\frac{\pi x}{4} \right)}}$

   The result is: $- \frac{\left(\frac{\pi \sin^{2}{\left(\frac{\pi x}{4} \right)}}{4} + \frac{\pi \cos^{2}{\left(\frac{\pi x}{4} \right)}}{4}\right) \sin{\left(2 x \right)}}{\cos^{2}{\left(\frac{\pi x}{4} \right)} \tan^{2}{\left(\frac{\pi x}{4} \right)}} + 2 \cos{\left(2 x \right)} \cot{\left(\frac{\pi x}{4} \right)}$

2. Now simplify:

   $$\frac{- \frac{\pi \sin{\left(2 x \right)}}{2} - \sin{\left(x \left(2 - \frac{\pi}{2}\right) \right)} + \sin{\left(x \left(\frac{\pi}{2} + 2\right) \right)}}{1 - \cos{\left(\frac{\pi x}{2} \right)}}$$

The answer is:

$$\frac{- \frac{\pi \sin{\left(2 x \right)}}{2} - \sin{\left(x \left(2 - \frac{\pi}{2}\right) \right)} + \sin{\left(x \left(\frac{\pi}{2} + 2\right) \right)}}{1 - \cos{\left(\frac{\pi x}{2} \right)}}$$