f(x)=4x^2 -6x +7
f(x+h)=4*(x+h)^2 -6(x+h)+7
=4x^2 +8hx +4h^2 -6x -6h +7
math-men define derivativ=limit at h gotu 0 av f(x+h) -f(x)
for this zampel, ...(4x^2 -4x^2) & (-6x +6x) & (7-7) kansel
that leev yu with 8hx-6 +4h^2
but as h gotu 0, h^2 go awae
derivativ=8x-6