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In rectangular ABCD, points E and F are on line AB and ad respectively, AE = EB = AF = 2 / 3fd = 4. Along the straight line EF, the triangle AEF is folded into triangle a'ef, Make plane a'ef perpendicular to plane bef Finding a '- fd-c cosine of dihedral angle If the points m and N are on the line segments FD and BC respectively, and the quadrilateral mncd is folded upward along the line Mn, so that C and a 'coincide, the length of the line segment FM is calculated
As shown in the figure, the total area of ABCD is 24,
Therefore, the area of the parallelogram efgh is 24-10 = 14
However, sphe + SPFG = 1 / 2sefgh = 7
So,
Area of aeph + area of pfcg = 7 + 6 = 13
So the area of quadrilateral pfcg is 13-5 = 8
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