1. T

    trigonometric identity

    cosA + cos(A + B) + cos(A + 2B) + cos(A + 3B) +...+cos{A +(n-1)B} = sin nB/2 ---------- . cos{A + (n-1)B/2} sin B/2 Can anyone kindly show me a way to prove this? Yours truly, TG
  2. A

    Is it a new identity or wat ??

    HI friends, I just found(kinda eureka :wink: rather it ccrossed my mind while doin somethin else) this... cosec^2 (x) + sec^2(x) = cosec^2 (x) * sec^2(x) seems to b interestin an queer to me... i don know if ths s anythin worthy or wat any comments Cheers Arun
  3. N

    Cotangent Identity

    Can someone show me why this identity is true? Pi*ctn(Pi*x) = Sum n from - infty to + infty (1/(x-n)) Thanks
  4. S


    Develop the identity for sin x sin y