recalling that a triangle has a sum of interior angles to be 180°, for an equilateral triangle that also means an equiangular triangle, so all angles are equal, that means each angle is 60°.
a square has each interior angle at 90°.
what's their ratio?
[tex]\bf \cfrac{triangle}{square}\qquad \qquad \cfrac{60}{90}\implies \cfrac{6}{9}\implies \cfrac{2}{3}[/tex]
