00:02
In this problem, we're given an equation which represents the area of the pupil of the eye, and we're looking at the sensitivity to light as the brightness increases.
00:11
And the way we find the sensitivity is by taking the derivative of the area of the radius.
00:17
And so we're going to use the quotient rule to get this derivative, since we have a quotient.
00:21
So here we have the bottom times the derivative of the top, minus the top times the derivative of the bottom over the bottom squared.
00:29
And now we can simplify that.
00:32
So what we do is we distribute the 9 .6 x to the negative 0 .6 power, and we distribute the 1 .6 x to the negative 0 .6 power.
00:43
And in the next step, we notice that we can cancel these opposite terms, and then we can add these like terms together.
00:52
And so for the derivative, we end up with negative 54 .4 over x to the 0 .6 power times 1 .1 plus 4 times x to the 0 .4 .4.
01:04
Squared.
01:05
That's a mouthful...