00:01
Now that we know how to
calculate the gradients
of tangents and normals.
00:06
We can move at one step further.
00:08
We can now start to look at
equations of tangents and normals.
00:12
So we are extending our ideas
or concepts of differentiation
to gradients of tangents
and normals.
00:19
And now we are going to learn
how to find the equations
of tangents and normals.
00:23
Now there's a little bit of
background that we are going
to discuss before.
00:27
And then we'll move forward to
actually doing some examples
and giving you a chance to work
some of them out yourself.
00:33
So we've previously discussed
what a tangent and a normal is.
00:37
So a tangent if I'm looking for
a gradient at a point P here,
the tangent runs along it.
00:45
So this here is your tangent.
00:47
And the normal meets
at 90 degrees there.
00:55
Once you know the gradient
of the tangent.
00:57
So if we just focus for a moment
on our tangents, once you know
the gradient of this, you can
from here calculate the actual
equation of the line of
the tangent.
01:10
Now you may have already
studied this before.
01:14
But the equation of
a straight line ...
01:23
follows the basic
structure of y = mx + c.
01:29
Let me just remind
you everything here.
01:34
y and x are two points
that the line goes through.
01:38
So any points.
01:39
Okay, so the line passes
through these two points.
01:42
Passes through.
01:45
And here m is your gradient.
01:49
So that's your gradient.
01:51
So that's quite important
for us to find out.
01:53
And c here is your y intercept.
01:55
So when the line
crosses the y intercept.
01:58
That is your c point.
02:00
And again that's really
important if you are
extrapolating any types of
line to get results on curves
describing decay or growth
within any type of medical field.
02:11
So if I drew an x-y axis here.
02:18
Let's call this x.
02:20
Let's call this y.
02:21
And if I extended this line,
this point here would be your c.
02:26
So make sure you remember this.
02:29
And you familiarize yourself
with this little idea here
of y = mx + c.
02:35
It's really quite important
not just in mathematics
but in physics and engineering.
02:39
It's almost a prerequisite for
any type of mathematical field
that you understand what
a general equation
of a straight line is.
02:46
And the tangents and the normals
obviously follow
the same format.
02:51
Now there is a different way
of writing it that
some of you may prefer.
02:55
And when we do the examples,
you can have a look at both.
02:57
And that is this, you
got y - y1 = m(x-x1).
03:04
It takes some practice of doing
these questions to actually
start appreciating
this method here.
03:09
Because this equation actually
includes the calculation for
your gradient here when you are
dealing with a straight line.
03:17
So you can actually just
calculate what the m is.
03:20
Whereas, in this equation you
have to this equation here.
03:23
You have to calculate
your m first.
03:25
Then you put it into this
equation and then find c.
03:29
But both methods are fine.
03:31
Both methods are valid.
03:32
This might be, this method here
might be just a few seconds
faster than the other.
03:38
But both of them are fine.
03:39
But the most important thing
is that you understand
the importance of this equation
or the format of this equation.
03:46
Because often you're given
questions in this form.
03:49
And it's important you
understand where the m is
and where the c is.
03:53
And with this equation it
usually is a lot more
difficult to do that.
03:56
And you often have to rearrange
this equation in order
to write this in y = mx + c.
04:03
So you can manipulate where
you gradient is
and where your intercept is.