Arthur D. answered 11/06/14
Tutor
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Forty Year Educator: Classroom, Summer School, Substitute, Tutor
from the midpoint of the diagonal draw a line down perpendicular to the bottom edge
this measure is 3 cm and is one leg of a right triangle
the other leg is half the measure of the bottom edge which is also 3 cm
the hypotenuse of this triangle is half the measure of the diagonal
let "h" be this measure
h=√(9+9)
h=√9*2
h=3√2
this measure and the length of one edge are the legs of another right triangle whose hypotenuse is the distance from the midpoint of the face diagonal to the bottom furthest vertex
let d=this distance
d2=62+(3√2)2
d2=36+18
d2=54
d=√54
d=3√6 cm