00:02
Okay, so we want to use the idea of differentials to estimate the value of this expression, 4th root of 624.
00:13
So since we have a 4th root, so our starting point will be, we'll start by taking the function to be 4th root of x, which is actually x to the part of 1 4th.
00:29
And also we will find the derivative of this function, f -dash of x, using the power rule.
00:38
So we have one -fourth, x to the power of one -fourth minus one.
00:45
And this gives us one -fourth, x to the part of negative 3 over 4.
00:55
Now, by the idea of differentials, we have this, we know this following relation, that f of a plus d x is approximately equal to f of a plus f dash evaluated at the point a multiplied by d.
01:24
So we want to find a such that a should be a number as close as possible.
01:30
To the number in question 624 so that a has a perfect 4th root so we see that in this case our choice of a is very nicely it is 625 because if you calculate f of a which is f of 625 this 4th root of 6 to 5, this turns out to be 5 by very straight calculation in the calculator.
02:11
And also we need this left side expression inside the function is value.
02:19
A plus d x, we need that to be 624, the number of those 4th root we are trying to estimate.
02:31
And since a is already 625, so my obvious value of d of x, turns out to be negative 1.
02:42
So now taking all these things together in this given expression, so we have f of 625 plus d of x which is negative 1 approximately equal to f of 625 plus f dash of a.
03:10
So if that we have found out on the top 1 4th now this has to be evaluated at a...