So, the triangle is equilateral, all its sides are equal⇒
AB=BC=AC=8
In an equilateral triangle, the height is also the median, so it divides the sides into 2 equal parts⇒
AO=OC=8:2=4
by the Pythagorean theorem
[tex]8^2=4^2+BO^2\\BO^2=64-16\\BO=\sqrt{48} \\BO=4\sqrt{3}[/tex]
Answer: BO=4√3
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P.S. Hello from Russia :^)