25-gon

 The golden ratio and the 25-gon

Regular polygons: nonagon

 Visual geometry: the regular nonagon

Square root 3 in a nonagon

Nonagon: lines of 1, 2 and square root 3 in a nonagon

odd numbers times 3,

 Odd numbers times three, 3x , x=odd number, 9,15,21,27,111

The square root of two

An interesting right angle triangle with sides: 1/2√5 , 1/2√3 and the hypotenuse √2

 

The square root of 2 and the golden ratio