Let's say that
Suppose the solution to the equation in part (d) is
If we look at the
secant line running through (0, ln 5) and (a, ka + ln 5), we see graphically that the gradient of the secant is
smaller than that of the tangent from the previous part.
Mathematically,
But, we also see that the gradient is always greater than 0, because
So, g is an increasing function for all positive x values, which means