Make a sketch. Let ABCD be the given isosceles trapezoid. The bases are AB = 22 cm long; CD = 10 cm; the lateral sides are AD = BC = 10 cm.Draw the perpendiculars CE and DF from the vertices C and D to the base AB. It is clear that the right-angled triangles ADF and BCE are congruent. Then the segments AF and BE have the length = = = 6 cm each. The height of the trapezoid CE is the leg of the right angled triangle BCE and its length is equal to = = = 8 cm. Now from the right-angled triangle AEC you have AC = = = = = = = . Thus the diagonal of the trapezoid AC is cm long. ANSWER