> f:= x -> x^4 -1;

> q:= (f(a+h) - f(a))/h;
secline:= x -> f(a) + q*(x - a);
m:= D(f)(a);
tanline:= x -> f(a) + m*(x - a);

> a:= 3;

> h:= 2;

> plot({f(x), secline(x), tanline(x)}, x = a-1..a+3, color=[blue,red,magenta]);