What steps were taken to get px-2x^2 to be p-4x??

I can't work out what happened to the 'x' after 'p'. I can see that 2x^2 equals 4x though.
Any help would be much appreciated :)
Thanks

2 answers

px - 2x^2
= x(p-2x) , when factored

If y = px - 2x^2
then dy/dx = p - 4x , if p is a constant

I don't understand what you mean by
"I can see that 2x^2 equals 4x though. "
2x^2 is NOT equal to 4x
Sorry I should have added that I was working it out as a derivitive