The derivative of a function f(x) is defined as
[tex]f'(x)=\displaystyle\lim_{h\to0}\frac{f(x+h)-f(x)}h[/tex]
For f(x) = 3x ² + 4, we have
[tex]f'(x)=\displaystyle\lim_{h\to0}\frac{(3(x+h)^2+4) - (3x^2+4)}h[/tex]
[tex]f'(x)=\displaystyle\lim_{h\to0}\frac{(3(x^2+2xh+h^2) - 3x^2}h[/tex]
[tex]f'(x)=\displaystyle\lim_{h\to0}\frac{6xh+3h^2}h[/tex]
[tex]f'(x)=\displaystyle\lim_{h\to0}(6x+3h) = \boxed{6x}[/tex]
