How would you differentiate 3x^4 - 2x^2 + 9x - 1

First we follow the "times by the power and take one from the power" rule. This is the easiest way to remember how to differentiate anything. 

So (3x4)x^(4-1) -(2x2)x^(2-1)+(9x1)x^(1-1) -(1x0)x^(0-1) gives us 12x³-4x¹+9- 0 

I hope that this is clear. Do you have any questions or something that is unclear?