Derivative of (1-5x)^4

1. Let $u = 1 - 5 x$.

2. Apply the power rule: $u^{4}$ goes to $4 u^{3}$

3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \left(1 - 5 x\right)$:

   1. Differentiate $1 - 5 x$ term by term:

      1. The derivative of the constant $1$ is zero.

      2. 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: $-5$

      The result is: $-5$

   The result of the chain rule is:

   $$- 20 \left(1 - 5 x\right)^{3}$$

4. Now simplify:

   $$20 \left(5 x - 1\right)^{3}$$

The answer is:

$$20 \left(5 x - 1\right)^{3}$$