Question

x^2/4,a=4 find the equation of the tangent line

Answer 1

Linear functions can be written as y=mx+b
Your tangent line will have that form.
m is f'(a)
b is the y-intercept of the tangent line
you can use f'(a) along with a point you know is on the line such as (a,f(a))
So you would do this to find b:
f(a)=f'(a)*a+b
f(a)-f'(a)*a=b
So we have b now.
Put back into the equation
y=f'(a)x+[f(a)-f'(a)*a]

Answer 2

Your first step is to find f'(x)