In the quadrilateral ABCD, ab = 2, radical 5, BC = 2, CD = 1, ad = 5, and angle c = 90 degrees, find the area of quadrilateral ABCD

There is Pythagorean theorem, so BD = BC squared + CD squared, then root = root 5
It can be verified that BD, AB and ad form right triangles, so the area of quadrilateral is the area of two right triangles
1 / 2 * 2 * 1 + 1 / 2 * radical 5 * 2 radical 5 = 6
*It's a multiplication sign

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