Summe und differenz von winkeln
`sin(α+β) = sin α * cos β + cos α * sin β`
`sin(α-β) = sin α * cos β - cos α * sin β`
`cos(α+β) = cos α * cos β - sin α * sin β`
`cos(α-β) = cos α * cos β + sin α * sin β`
`tan(α+β) = (tan α + tan β) / (1- tan α * tan β)`
`tan(α-β) = (tan α - tan β) / (1+ tan α * tan β)`
`cot(α+β) = (cot α * cot β - 1) / (cot β + cot α)`
`cot(α-β) = (cot α * cot β + 1) / (cot β - cot α)`