The slope of the tangent line is the first derivative. So:Originally Posted by tnkfub
(Note: If this doesn't look like the quotient rule, that's because it isn't. I rarely use the quotient rule because I can't ever remember the correct form. I always move the denominator up and use the product rule.)
Now, to find the slope at the point (2,4) we plug in the x value:
The equation for a line is y = mx + b. So we want the equation for the line with a slope of 0 that passes through the point (2,4). Thus:
Thus your line is y = 4.