00:01
So here, given the formula of y, we want to know the arc length on the interval from 0 to pi over 4.
00:09
Then we call the formula for the arc length is s equal to integral from 0 to pi or 4, and then square root of 1 plus y's derivative square d x.
00:25
Then first we will calculate the derivative of y, which is 1 over cosine x.
00:35
Times negative sine x, that is really negative tangent x.
00:44
Then let's look at the formula where it's 1 plus derivative y square, which is equals to 1 plus tangent x square.
00:58
This is 1 over cosine x square.
01:02
Then we get a perfect square for the formula, so that it can make the integral of us really easy.
01:09
So we will have s equals to the integral from 0 to pi over 4, and then the absolute value of 1 over cosine x, dx.
01:22
But then since x is in the interval from 0 to pi or 4, then cosine x is always positive in this interval...