Derivative of x*sin(pix/2)

1. Apply the product rule:

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

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

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

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

   1. Let $u = \frac{\pi x}{2}$.

   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 $\frac{d}{d x} \frac{\pi x}{2}$:

      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: $\frac{\pi}{2}$

      The result of the chain rule is:

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

   The result is: $\frac{\pi x \cos{\left(\frac{\pi x}{2} \right)}}{2} + \sin{\left(\frac{\pi x}{2} \right)}$

2. Now simplify:

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

The answer is:

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