คำตอบ - Derivative

Applying the sum rule of derivatives.

$$\frac{d}{dx}[x+y]=\frac{d}{dx}\left[x\right]+\frac{d}{dx}\left[y\right]$$

The derivative of a variable with respect to itself is always equal to one.

$$\frac{d}{dx}\left[x\right]+\frac{d}{dx}\left[y\right]=1+\frac{d}{dx}\left[y\right]$$