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Happy Valley Grade 5 winter vacation homework Mathematics Page 14 The answer to the second small question of brain engine.
Connect BH, let HD=X, then AH=AD-X, SYN = S (HGD)+S (BEH)+S (BFH).

Where BEH is a triangle with BE as the base and DC as the height, which can be obtained;

BFH is a triangle with BF as the base, AD-X as the height, HDG is a triangle with DG as the base and X as the height, DG=BF, so add them together and eliminate X, and the result will come out.