Chapter 5: Introduction to Euclid's Geometry

Exercise 5.1 - Solutions

Question 3

How many lines pass through two distinct points?

One and only one line (Euclid's 1st postulate)


Question 4

If AC=BDAC = BD, prove AB=CDAB = CD

Given: AC=BDAC = BD

AC=AB+BCAC = AB + BC BD=BC+CDBD = BC + CD

Since AC=BDAC = BD: AB+BC=BC+CDAB + BC = BC + CD

Subtracting BCBC (Axiom 3): AB=CDAB = CD