### Video Transcript

Find the length of the
perpendicular drawn from the point π΄ one, nine to the straight line negative five
π₯ plus 12π¦ plus 13 equals zero.

So weβre going to answer this
question using the formula for calculating the distance between a point and a
straight line. So the formula is this. If I have the straight line with
equation ππ₯ plus ππ¦ plus π is equal to zero and I have a point with coordinates
π₯ one, π¦ one. Then the perpendicular distance
between them, π, is given by the modulus of ππ₯ one plus ππ¦ one plus π, all
divided by the square root of π squared plus π squared. So what I need to do is determine
the values of π, π, π, π₯ one, and π¦ one and then substitute them into the
formula.

Letβs look at the straight line
first of all. Iβm comparing it with ππ₯ plus
ππ¦ plus π is equal to zero. This shows me that π is equal to
negative five, π is equal to 12, and π is equal to 13. Now letβs look at the point π΄,
which has coordinates one, nine. This tells me that π₯ one is equal
to one and π¦ one is equal to nine. So now I have all the values I
need. And itβs just a case of
substituting them into this formula for the distance π.

So we have that π is equal to
negative five times one plus 12 times nine plus 13, the modulus of that
quantity. Then weβre going to divide it by
the square root of negative five squared plus 12 squared. This gives us the modulus of
negative five plus 108 plus 13 all divided by the square root of 25 plus 144. This gives the modulus of 116 over
the square root of 169. Now as 116 is positive, then its
modulus is just its own value. So the numerator will be 116. And in the denominator, the square
root of 169 is 13 exactly.

So we have our answer to the
problem. The length of the perpendicular
between the point one, nine and the straight line negative five π₯ plus 12π¦ plus 13
equals 0 is 116 over 13.