To make an equation for a tangent line we need a slope and a point. The slope at x = 1 is 2 and our point is (1,4).
f(1)=4 tells us we have a y value of 4 when we have an x value of 1; hence (1,4)
f '(1) = 2 tells us we have a slope of 2 when x = 1.
so:
y - 4 = 2(x - 1) (this is the answer)
