00:01
So in this question, they ask us, what is a formula for the second derivative of f of t, which is t -square times the sign of 2t? then we're going to use that formula to compute f -double prime of pi over 2.
00:16
So if i want derivatives of f -of -t equals t -square times the sine of 2t, i'm going to need the product rule, big picture.
00:27
So what's my first derivative looking like? well, i've got my first factor, t -square.
00:34
Times the derivative of the second factor, my derivative of the sine of 2t is the cosine of 2t times 2 by the chain rule, 2 cosine of 2t, plus my second factor, the sign of 2t, times the derivative of the first factor, my derivative of t squared, that's 2t.
01:03
And so cleaning up my first derivative, i've got 2t squared times the cosine of 2t plus 2t times the sign of 2t.
01:21
Now let's get my second derivative, f double prime.
01:27
Now again, if i want my derivative of 2t squared cosine of 2t, i'm going to need the product.
01:33
I take my first factor 2t squared times the derivative of the second.
01:40
My derivative of the cosine of 2t is negative 2, sine of 2t, plus my second factor, cosine of 2t times the derivative of the first factor, my derivative of 2t squared.
02:01
That's 4t...