If `α/2` is in the first or fourth quadrants, the formula uses the positive case: `cos (alpha/2)=sqrt((1+cos alpha)/2` If `α/2` is in the second or third quadrants, the formula uses the negative case: `cos (alpha/2)=-sqrt((1+cos alpha)/2` Half Angle Formula - Tangent . The tangent of a half angle is given by: `tan (alpha/2)=(1-cos alpha)/(sin $\map \tan {a - b} = \dfrac {\tan a - \tan b} {1 + \tan a \tan b}$ Sum of Squares of Sine and Cosine $\cos^2 x + \sin^2 x = 1$ Corollary 1 $\sec^2 x - \tan^2 x = 1 \quad \text {(when $\cos x e 0$)}$ Corollary 2 $\csc^2 x - \cot^2 x = 1 \quad \text {(when $\sin x e 0$)}$ Double Angle Formulas Double Angle Formula for Sine Here, tan(θ 2) = sinθ = 2tan(θ 2) 1 + tan2(θ 2) So, tan( θ 2)((1 + tan2( θ 2) − 2) = 0. And so, tan(θ 2) = 0 gives θ 2 = kπ,k = 0,1,2,3,.. the other factor = 0 gives# tan^ (theta/2)=1 to tan (theta/2)=+-1 to. theta/2=kpi+-pi/4#. Combining both for values of θ ,. θ = 2kπ and θ = (2k ± 1 2)π,k = 0,1,2,3, Answer link. Jun 28, 2016. We use the formula :tan(A −B) = tanA− tanB 1 +tanAtanB. ∴ tan(180o −a) = tan180o −tana 1 + tan180o ⋅ tana. But, tan180o = 0. Hence, we get tan(180o −a) = −tana. Answer link. We use the formula : tan (A-B)= (tanA-tanB)/ (1+tanATanB). :. tan (180^o-a)= (tan180^o-tana)/ (1+tan180^o*tana). But, tan180^o=0. Vay Nhanh Fast Money.

2 tan a tan b formula