Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Construct with a ruler and compass a square, given one point from each side.

Square Deal

I was reading the answer to Square Deal, and I do not understand how the rest is easy to solve. Could someone help me understand? I don't see the square.

share|cite|improve this question
@Freddy, if it's not a Euclidean space, then what's a square? – Gerry Myerson Jan 20 '13 at 10:15
Ah, Ok, I overlooked it. – 007resu Jan 20 '13 at 10:57
It would be useful to include the partial solution given in the link, both for the convenience of readers here, and to prevent link rot. – Travis Sep 16 '15 at 3:24
up vote 6 down vote accepted

Connect $A$ and $C$ and draw a perpendicular from $B$ to this segment. Now construct $D’$ on this perpendicular such that $AC = BD’$. $DD'$ is one side of the square. (This construction is already given in the link provided)

Now to complete the square, draw perpendiculars from point $A$ and $C$ to the line $DD'$. And then draw a line passing though $B$ parallel to $DD'$.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.