00:01
In this question, we are given the function y is equal to sine x squared plus 1, and we're asked to demonstrate that the derivative of y with respect to x is the same, whether we think of y as a composite of these two functions, or as a composite of these two slightly different functions.
00:29
So for part a, we're considering the function x squared to be the variable u, and then considering y to be the function sine of u plus one.
00:41
And then part b we call x squared plus one the variable u and take y to be the sign of you.
00:56
So for both questions we can say, or for both parts, we can say that d y d x by the chain rule is equal to d y d u times d u d x.
01:14
That's true in general.
01:16
That's the chain rule.
01:17
It always applies, except if it doesn't allow, except if it's mathematically impossible, like dividing by zero.
01:29
So we can apply this fact to part a and then to part b...