00:01
They want us to find f prime of a of the function f of x is equal to the square root of one minus two x and i'll recall that f prime of a is equal to the limit as x approaches a of f of x minus f of a all over x minus a so let's go ahead and plug everything in now and see if we could do a little bit of algebra to help us be able to evaluate this limit so f of x is going to be 1 minus 2x square root.
00:35
When we plug a in, the only difference is going to be root a now.
00:41
So 1 minus 2a all over x minus a.
00:47
Now the trick to evaluate this is we're going to multiply the top and bottom by the conjugate of what we have in the numerator.
00:54
So it's going to be 1 minus 2x square root plus square root of 1 minus 2a.
01:02
And we're going to do that same thing in the denominator, since we can only ever multiply a function by 1.
01:11
Now, after doing that, this being multiplied in the numerator is just the difference of squares.
01:21
So that should give us 1 minus 2x minus 1 minus 2a all over x minus x minus 1 minus a, times 1 minus 2x.
01:43
That should be square root.
01:46
Square root of 1 minus 2x plus the square root of 1 minus 2a.
01:54
And now these ones here should cancel out with each other.
02:03
And let's go ahead and rewrite this one more time.
02:09
Limit as x approaches a...