[tex]\text{Given that,}\\\\f(x) = 3x^2 -5x +4\\\\\\ \dfrac{f(a+h)-f(a)}{h}\\\\=\dfrac{3(a+h)^2 -5(a+h) +4 - (3a^2 -5a +4)}{h}\\\\=\dfrac{3(a^2 +2ah +h^2) -5a-5h+4-3a^2+5a-4}h\\\\=\dfrac{3a^2 +6ah +3h^2 -5a-5h-3a^2+5a}h\\\\=\dfrac{3h^2 +6ah -5h}h\\\\=\dfrac{h(3h+6a-5)}h\\\\=3h+6a-5[/tex]
