In trapezoidal ABCD, if ad ‖ BC, ∠ B = 90 °, C = 45 °, CD = 10cm, BC = 2ad, the area of trapezoid is______ cm2．

If we make de ⊥ BC at point e through point D, then the quadrilateral abed is rectangle ⊥ ad = be, de = ab ∵ BC = 2ad ⊥ be = EC ∵ C = 45 °⊥ CDE is isosceles right triangle ⊥ CE = de = ad = be = ab ⊥ CD = 10cm ⊥ CE = de = ad = be = AB = cdsin45 ° = 52 ⊥ BC = 102 ⊥ trapezoid area = 12 (AD + BC) · AB = 12 × 152 × 52 = 75cm2

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