三角恒等變換公式是解決三角函數(shù)問題的基礎(chǔ)，包括和差角公式、積化和差公式、倍角公式等。其中，正弦函數(shù)、余弦函數(shù)、正切函數(shù)的恒等變換公式如下

正弦函數(shù)：sin(-x) = -sin(x)sin(x + π) = -sin(x)sin(x + 2π) = sin(x)sin(x + π/2) = cos(x)sin(x - π/2) = -cos(x)

余弦函數(shù)：cos(-x) = cos(x)cos(x + π) = -cos(x)cos(x + 2π) = cos(x)cos(x + π/2) = -sin(x)cos(x - π/2) = sin(x)

正切函數(shù)：tan(-x) = -tan(x)tan(x + π) = tan(x)tan(x + π/2) = -cot(x)tan(x - π/2) = cot(x)。