Does the similar figures theorem apply also to altitudes and medians?

1 Answer
Apr 26, 2018

Yes.

Explanation:

A similar figure is a figure that is geometrically the same.

In the case of triangles, two triangles are similar if their sides are proportionate.

I assume we are talking about the theorem of scaling.

If we have a triangle and we scale by a factor ab, all sides of the scaled triangle will be increased by ab.

Since a triangle is uniquely defined by the length of its sides, all angles will remain the same and consequently the altitude will increase by ab

The medians will still be in the same relative position, by definition of a median. The length from a vertex to the opposite side will increase by the factor ab. ( this is a linear measurement )

The easiest way to see this is:

All linear measurements i.e. length will increase by ab, all quadratic measurements will increase by (ab)2 and all cubic measurements will increase by (ab)3. Angular measurement remain unchanged by scaling, these are non linear, non quadratic and non cubic.

As an example:

Given an equilateral triangle with sides 4.

Scaled by a factor 12

Altitude of triangle:

4222=12=23

After scaling by 12:

sides=2

Altitude of scaled triangle:

2212=3

Notice this is:

12×23=3

Notice area:

Area of original triangle:

12(4)×23=43

Area of scaled triangle:

12(2)×3=3

(12)2×43=14×43=3

As you can see the area is quadratic, so we used (ab)2

Don't know whether this helps you.