Known: as shown in the figure, ∠ B = ∠ d = 90 °, a = 60 °, ab = 4, CD = 2

Extend ad, BC, intersect at the point E, in RT △ Abe, ∠ a = 60 °, ab = 4, ｜ e = 30 °, AE = 2Ab = 8, ｜ be = ae2-ab2 = 43, in RT △ DCE, ∠ e = 30 °, CD = 2, ｜ CE = 2CD = 4, according to Pythagorean theorem: de = ce2-cd2 = 23, then s quadrilateral ABCD = s △ abe-s △ DCE = 12ab · be-1

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