Errors Trigonometry and Sets

Find the error

(SinA +Sin3A)/(CosA +Cos3A) = Tan 2A

Show that (SinA +Sin3A)/(CosA +Cos3A) = Tan 2A

Applying Tan(A-B)

Applying tan(A+B)

Graph of Trigonometric Functions (I)

Graph of y = Sin(x)  0≤x≤P

Graph of y = Sin2x,  0≤x≤P

Graph of y = Sin3x  0≤x≤P

Prove that 2 Cos (Pi/13). Cos (9Pi/13) + Cos (5Pi/13) + Cos (3Pi/13)= 0

Prove that 2 Cos (Pi/13). Cos (9Pi/13) + Cos (5Pi/13) + Cos (3Pi/13)= 0