What is realative error(hard one),give me the sine,cos rule

Relative error = maximum absolute error/actual value
sine formula,a/sinA = b/sinB = c/sinC = 2r
cosine formula,a² = b² + c² - 2bc cosA
Area of triangle= absinC/2 or a²sinBsinC/2sinA
another cosine formula,cosA = (b²+c²-a²)/2bc
If C=90 degree.then a² + b² = c²(Pyth.theorem)
用到既係咁多,其他沒實際作用