# Math Help - tangent lines

1. ## tangent lines

hey i need some help with tangent lines, i just dont understand it at all. I need to figure out how to find the equation of the tangent line to f(x)=x^3 at the point where x=3...much thanks

2. Originally Posted by mer1988
hey i need some help with tangent lines, i just dont understand it at all. I need to figure out how to find the equation of the tangent line to f(x)=x^3 at the point where x=3...much thanks
remember, a line is of the form $y = mx + b$ where $m$ is the slope, and $b$ is the y-intercept.

how do we find the slope? well, from the derivative of course. find $y'$ and plug in $x = 3$ to get the slope at that point, then use the point slope form.

$y = y_1 = m(x - x_1)$

where $(x_1,y_1)$ is the point on the graph when $x = 3$

just solve for y to get the equation of the line