Question

demonstrati:
sin($\frac{ \pi }{2} + x$)=cosx;
cos($\frac{ \pi }{2} + x$)=-sinx

Answer 1

[tex]sin ( \frac{ \pi }{2} - x) = sin( \frac{ \pi }{2}) cosx - sin x cos ( \frac{ \pi }{2} ) [/tex]

Dar [tex]sin ( \frac{ \pi }{2} ) = 1 [/tex]  si $cos ( \frac{ \pi }{2} ) = 0$ ⇒ $sin ( \frac{ \pi }{2} - x) = cos x$

Analog pentru $cos ( \frac{ \pi }{2} - x) = sin x$