三角恒等变换公式是解决三角函数问题的基础，包括和差角公式、积化和差公式、倍角公式等。其中，正弦函数、余弦函数、正切函数的恒等变换公式如下

正弦函数：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)

余弦函数：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)

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