# Thread: Equation of tangent line

1. ## Equation of tangent line

I have a homework question in which im supposed to find an equation of the tangent line to the graph at the point (1, f(1)). How would i do this>> I found the derivative and found the zeros of the derivative (which are the points on the graph at which the tangent line is horizontal) How do i use this to find it at (1, f(1))? Thank you!

2. Originally Posted by nascar77
I have a homework question in which im supposed to find an equation of the tangent line to the graph at the point (1, f(1)). How would i do this>> I found the derivative and found the zeros of the derivative (which are the points on the graph at which the tangent line is horizontal) How do i use this to find it at (1, f(1))? Thank you!
equation of the tangent line at the point $\displaystyle (1, f(1))$ is ...

$\displaystyle y - f(1) = f'(1)(x - 1)$

3. substitute 1 into the derivitive and this will give you the gradient. use that value as m in y=mx+c and also substitute in your x and y values (1;f(1)) to solve for c.