Question

How did 2400x-2x^2 became

dA/dx= 2400-4x?

Answer 1

if y = a x^n

then
dy/dx = a n x^(n-1)

so if
y = 2400 x^1 - 2 x^2
then
dy/dx = 2400 (1) x^(1-1) - 2 (2) x(2-1)
or
dy/dx = 2400 x^0 - 4 x^1
which is
dy/dx = 2400 - 4 x