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From Pythagorean theorem: ((1/2)a)^2 + h^2 = a^2, (1/4)a^2 + h^2 = a^2, h^2 = a^2 - (1/4)a^2, h^2 = (3/4)a^2, h = square root of ((3/4)a^2), h = ((square root of 3) / 2) a.