As shown in the figure, EF is the double fold line of square ABCD, and the vertices of ∠ A and ∠ B coincide on EF. At this time, how many degrees is ∠ DHG?

Because DG, GC and CD are equal to the side length of square ABCD, DG = GC = CD. So ∠ GDF = 60 °. Because ∠ ADF = 90 °, so ∠ ADG = ∠ ADF - ∠ GDF = 90 ° - 60 ° = 30 °. From the folding, it can be seen that ∠ HDG = 12 ∠ ADG = 12 × 30 ° = 15 °; ∠ HGD = ∠ a = 90 °. In △ HDG, from the sum of internal angles of triangles is 180 °, we can get ∠ DHG = 180 ° - ∠ HDG - ∠ HGD = 180 ° - 15 ° - 90 ° = 75 °. Answer: at this time ∠ DHG is a square 75 degrees

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