Integral of 45x dx

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

   $$\int 45 x\, dx = 45 \int x\, dx$$

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

      $$\int x\, dx = \frac{x^{2}}{2}$$

   So, the result is: $\frac{45 x^{2}}{2}$

2. Add the constant of integration:

   $$\frac{45 x^{2}}{2}+ \mathrm{constant}$$

The answer is:

$$\frac{45 x^{2}}{2}+ \mathrm{constant}$$