If `x_n=cos(pi/4^n)+isin(pi/4^n)`, then `x_1.x_2.x_3.................oo`

If x_(n)=cos((pi)/(4^(n)))+i sin((pi)/(4^(n))), then x_(1)*x_(2),x_(3)...............oo

If x_(n)=cos(pi/3^(n))+isin((pi)/(3^(n))) , then x_(1),x_(2),x_(3),………………..x_(infty) is equal to

If x_(n)=cos(pi/2^(n))+isin(pi/2^(n)), n in N then x_(1),x_(2),x_(3)………………..x_(infty) . Is equal to

If x_n =cos ((pi)/(2^(n)))+isin((pi)/(2^(n))) Prove that x_1 x_2…..x_oo=-1

If x_(n)=cos(pi)/(2^(n))+i sin(pi)/(2^(n)), prove that x_(1)x_(2)x_(3)x_(oo)=-1

If f(x) is given by f(x)=(cosx+i sinx)(cos3x+isin3x) ......... ....... [cos(2n-1)x+isin(2n-1)x] , then f''(x) is equal to