Integral of 20x^3dx dx

1. The integral of a constant times a function is the constant times the integral of the function:

   $$\int 20 x^{3} \cdot 1\, dx = 20 \int x^{3}\, dx$$

   1. The integral of $x^{n}$ is $\frac{x^{n + 1}}{n + 1}$ when $n \neq -1$:

      $$\int x^{3}\, dx = \frac{x^{4}}{4}$$

   So, the result is: $5 x^{4}$

2. Add the constant of integration:

   $$5 x^{4}+ \mathrm{constant}$$

The answer is:

$$5 x^{4}+ \mathrm{constant}$$