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1.角的拼凑 适当地变化角的表达式,可以给三角函数 求值带来便利.如单角a可以看成角α+β与角 β的差,也可以看成角α-β与角β的和,既可以 看成是α/2的二倍,也可以看成是2α的一半.角 的分拆与配凑也是变角的常用策略.如2α=(α +β)+(α-β),α-β=2α-(α+β)等.当条件 所给角都是非特殊角时,要仔细观察非特殊角
1. The patchwork of angles appropriately change the expression of the angle, which can bring convenience to the evaluation of the trigonometric function. If the single angle a can be seen as the difference between the angle α+β and the angle β, it can also be seen as the angle α-β and the angle The sum of β can be regarded as a double of α/2, and can also be regarded as a half of 2α. The splitting and matching of angles is also a common strategy of changing the angle. For example, 2α=(α+β)+(α) -β), α-β = 2α-(α + β), etc. When the conditions given are all non-special angles, look carefully for non-special angles.