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2 ???????? 22 s i n)s i n1(??? 2s i n21???? 2s i n212c o s1c o s22c o s 2 ????22c os1s i n 2 ???? 22c os1c os 2 ????公式左端的角是右端角的二倍 在這兩個(gè)公式中分別求出 sin2a和 cos2a 靈活 運(yùn)用公式 ???? 2c o s2s i n24s i n2c os2s i n2s i n????????? 22 s i nc o s2c o s???? c o ss i n22s i n4xs i n4xc os2xc os 22 ??4xs i n21 2?? 14xc os2 2 ???8s in ?? ?21s in ???3c o s ???6c o s ?????? 2s i n212c o