The teachers’ library›TrigonometryDouble angle formulassin2θ=2sinθcosθsin2θ=2sinθcosθcos2θ=cos2θ−sin2θcos2θ=cos2θ−sin2θcos2θ=2cos2θ−1=1−2sin2θcos2θ=2cos2θ−1=1−2sin2θtan2θ=1−tan2θ2tanθtan2θ=2tanθ1−tan2θOpen on a new board The board is kept in this browser only, like your other boards. On any board, the Library button adds this too.More in TrigonometrySOH CAH TOAPythagorean identitiesReciprocal trigonometric functionsExact valuesCompound angle formulasHalf-angle and power-reducing formulasSum-to-product formulasCofunction and symmetry identitiesGeneral solutions of trigonometric equationsRadians and degrees