三角求值、化简、证明是三角的主要题型，在所有的三角问题中，以“变”为主线，通过一系列的“变角”、“变名”、“变次”、“变结构”等方法来解决问题。%Evaluation, simplification and proving are main types of problems about trigonometric functions, which can be solved through a series of"changes", including"the change of angles","the change of names","the change of powers", and"the change of structures".
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