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Question:
plz explain how is tan(π+π/2)=tan π/12 and how does tan repeats itself after every π and sin,cos repeat after every π
Answer:

1. tan (Π + Π/2) = tan(Π/2)

tan (Π + θ) = tan(Π/2 + Π/2 + θ)

                   = tan{Π/2 + (Π/2 + θ)}

                   = - cot(Π/2 + θ)                    (Since tan(Π/2 + θ) = - cotθ )

                   = -{- tanθ}                           (Since cot(Π/2 + θ) = - tanθ)

                   = tanθ

=> tan (Π + θ) = tanθ

Now put θ = Π/2

So tan (Π + Π/2) = tan(Π/2)

2. sin (Π + θ) = sinθ

sin (Π + θ) = sin(Π/2 + Π/2 + θ)

                   = sin{Π/2 + (Π/2 + θ)}

                   = cos(Π/2 + θ)                    (Since sin(Π/2 + θ) = cosθ )

                   = - sinθ                           (Since cos(Π/2 + θ) = - sinθ)

=> sin (Π + θ) = - sinθ

3. cos (Π + θ) = - cosθ

cos (Π + θ) = cos(Π/2 + Π/2 + θ)

                   = cos{Π/2 + (Π/2 + θ)}

                   = - sin(Π/2 + θ)                    (Since cos(Π/2 + θ) = - sinθ )

                   = - cosθ                           (Since sin(Π/2 + θ) = cosθ)

=> cos (Π + θ) = - cosθ 

In this way sin, cos and tan repeat itself after every Π. 

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