Question

What is an equation of the tangent line at x = 4, assuming that f(4) = 3 and f '(4) = 2? (enter your answer as an equation using the variables y and x.)?

Answer 1

The general equation for a line in the case where the slope and one point on the line are known is y-b = m(x-a), where m is the slope and (a,b) is the point.

Here f(4) = 3 corresponds to the point (4,3), and f '(4) = 2 corresponds to the slope of the tangent line at that point.

Thus the equation of the tangent line here is

y - 3 = 2(x - 4).

An alternative form of this equation would be y = 3 + 2x - 8, or

y = 2x - 5