If a triangle is not equilateral, must its orthocenter and circumcenter be distinct?

625 Views Asked by At

According to Proof Wiki, if a triangle is not equilateral, then its orthocenter and circumcenter must be distinct. The exact quote is

Let △ABC be a triangle.
Let O be the circumcenter of △ABC.
Let G be the centroid of △ABC.
Let H be the orthocenter of △ABC.

Then O, G and H are the same points if and only if △ABC is equilateral.
If $\triangle ABC$ is not equilateral, then $O, G$ and $H$ are all distinct.

Well, it looks like I've found a counterexample: $$A=(0,0),\quad B=\left(1-\frac{\sqrt 3}{2},\frac12\right),\quad C=\left(1-\frac{\sqrt 3}{2},-\frac12\right)$$

and the orthocenter and circumcenter both coincide at $(1,0)$, right?

So is my counterexample valid, or did I screw something up?

2

There are 2 best solutions below

5
On BEST ANSWER

In your example, the orthocentre is $(-\sqrt{3},0)$ and the circumcentre is $(1,0)$.

0
On

In your example, the circumcentre is $(1,0)$, the centroid is $\left(\frac13\left(2-\sqrt3\right),0\right)$ and the orthocenter is $\left(-\sqrt3,0\right)$.