In quadrilateral BCED, we have BD = 11, BC = 9, and CE=2. Sides BD and CE are extended past B and C, respectively, to meet at point A. If AC = 8 and AB = 5, then what is DE?
There are two different triangles: ΔABC and ΔADE These triangles share the same angle, ∠BAC or ∠DAE
1) Use the Law of cosines to calculate an angle BAC of a triangle ABC.
2) Use the Law of cosines to find the length of DE.