The height, h, of an equilateral triangle of side length 1m is √(1-0.5^2)=√0.75=0.866m approx. because the perpendicular from the vertex bisects the base. So we have a right-angled triangle and we can apply Pythagoras' Theorem: h^2=1^2-0.5^2, h=√(1-0.5^2).