ABCD is a parallelogram. EF is parallel to AB and the cord AC crosses line EF at X Where AB=12cm      AE=2cm      ED=8cm Calculate the length XF

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Triangle AEX is a similar triangle with triangle ADC exterior angles on the same side of a transversal are equal and AD and AC are transversals cutting across the two parallel lines EF and DC.  Angle EAX and Angle DAC are the same angle.  Thus the two triangles are similar by Angle, Angle, Angle.  Corresponding sides of similar triangles are proportional so:   length (EX) / 12 = 2 / 10 Solve for length EX by multiplying both sides of equation by 12 length EX = 2.4 XF = 12 - EX length = 12-2.4= 9.6