### Video Transcript

What is length ππ΅ rounded to the nearest hundredth?

Letβs look carefully at the diagram weβve been given. It consists of a right-angled triangle, triangle π΄π΅πΆ. Weβve been told the length of the hypotenuse. Itβs 10 centimeters. π is a point somewhere inside the triangle. And weβre asked to find the length of the line ππ΅.

Letβs first consider the line π΅π, which connects the right angle of the triangle to the opposite side. The blue lines on the two portions of π΄πΆ indicate that they are both the same length. And therefore π΅π is a median of the triangle. Specifically, itβs the median drawn from the right angle.

A key fact which you need to remember about the medians of right-angled triangles tells us that the length of the median from the vertex of the right angle is half the length of the hypotenuse. So we can calculate the length of π΅π. Itβs π΄πΆ over two. π΄πΆ is 10 centimeters, and therefore π΅π is five centimetres. So now we know the length of π΅π, but we want to calculate the length of ππ΅, which is just a portion of this line.

The question is how far along the length of π΅π is the point π. Letβs consider the other internal line in this triangle, the line π΄πΏ. As before, we can see that this line divides the opposite side of the triangle, in this case π΅πΆ, into two equal portions. And therefore π΄πΏ is also a median of the triangle. How does this information help? Well π is the point where these two medians intersect, which means it is the centroid or concurrence point of the triangle.

A key fact about the positioning of the centroid of a triangle is that it divides each median in the ratio two to one. The longer part of this ratio is always the part coming from the vertex of the triangle. So this means that the line segments ππ΅ and ππ are in the ratio two to one. Or phrased another way, we can conclude the ππ΅ is two-thirds of the total length of π΅π.

Weβve already calculated π΅π. Itβs five centimeters. And therefore we have all the information we need to now calculate the length of ππ΅. Itβs two-thirds multiplied by five, which is 10 over three. Remember, the question has asked us to give this length rounded to the nearest 100th. So as a decimal, this is 3.33 centimeters.

There were two key facts that we used about the medians of triangles. Firstly, that in a right-angled triangle, the length of the median from the vertex of the right angle is always half the length of the hypotenuse. Secondly, we used the fact that the centroid of the triangle, the point where the medians intersect, divides the median in the ratio two to one.