Marks' first lessons in geometry / In two parts. Objectively presented, and designed for the use of primary classes in grammar schools, academies, etc.

by Bernhard Marks

DEMONSTRATION.

We wish to prove that

The sum of any two sides of a triangle is greater than the third side.

Let the figure a b c be a triangle, then will the sum of any two sides, as a c, c b, be greater than the third side a b.

For the straight line a b is the shortest distance between the two points a and b, and is therefore less than the broken line a c b.

PROPOSITION IX. PROBLEM.

The following solution is so easy that you will understand it at once:—

We wish

To construct an equilateral triangle on a given straight line.