sin2x*cosπ/3+sin2x*cosπ/3=2*(sin2x*cosπ/3)
因为cosπ/3=1/2
所以sin2x*cosπ/3+sin2x*cosπ/3=sin2x
sin2x*cosπ/3+sin2x*cosπ/3 为什么等于sin2x
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