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- [Voiceover] Let F be a function such that
F of negative one is three.
And F prime of negative one is equal to five.
Let G be the function G of X
is equal to one over X.
Let capital F be a function defined as
the product of those other two functions.
What is capital F prime of negative one?
Well, we can just apply the product rule here,
let me just rewrite let me just
essentially state the product rule.
Capital F prime of X
is going to be equal to
since capital F of X is the product
of these two functions,
when we apply the product rule this is gonna be
F prime of X
times G of X
plus plus
F of X
times G prime of X.
And so if we want to evaluate this
at F of negative one
capital F prime
at negative one is equal to
F prime of negative one
times G of negative one
plus function F evaluated at negative one
times the derivative of G
evaluated at negative one.
And let's see if we can figure these things out.
So do they tell us this anywhere?
Can we figure this out?
F prime of negative one.
Well they tell us right over here
F prime of negative one
is equal to five.
So this is equal to five.
Now, let's actually stick with F.
What is F of negative one?
Well, they tell that to us
right over here.
F of negative one is equal to three.
So F of negative one is equal to three.
Now G of negative one
and G prime of negative one
they don't give it to us explicitly here
but we can figure it out.
We can, we know that if G of X
is equal to this
G of negative one is equal
to one over negative one
which is equal to negative one.
So this is equal to
negative one.
And then last but not least
if we want to find G prime of negative one
we just have to take the derivative of this.
So G prime of X.
Actually just let me rewrite G of X.
G of X
one over X is just the same thing
as X to the negative one.
So we're gonna use a power rule
to figure out G prime of X
is equal to bring that exponent
out front, negative one times X
to the and then decrement the exponent
negative two power.
So, G prime of
negative one
of negative one is equal to
negative one times
negative one to the
negative two power.
And that's just the same thing as
negative one over negative one squared.
This is one.
So this is just all going to evaluate
to negative one.
So this is
negative one.
And so we have
five times negative one
which is negative five.
Plus three times negative one
which is negative three.
Which is equal to
negative eight.
So F prime of negative one
is equal to negative eight.