Neka su
![a](/media/m/6/d/2/6d2832265560bb67cf117009608524f6.png)
,
![b](/media/m/e/e/c/eec0d7323095a1f2101fc1a74d069df6.png)
,
![c](/media/m/e/a/3/ea344283b6fa26e4a02989dd1fb52a51.png)
,
![d](/media/m/f/7/d/f7d3dcc684965febe6006946a72e0cd3.png)
realni brojevi takvi da vrijede jednakosti
![\begin{gather*}
2\cos a + 6 \cos b +7 \cos c+ 9 \cos d=0, \\
2\sin a-6\sin b +7\sin c -9\sin d=0.
\end{gather*}](/media/m/5/2/2/5225fe10fa480dee0a89f9ee6165c860.png)
Ako je
![\cos(b+c)\neq 0](/media/m/f/1/9/f19247dc4019c1a0b203d399fe98dfa5.png)
, odredi vrijednost izraza
![\displaystyle \frac{\cos(a+d)}{\cos(b+c)}](/media/m/6/d/3/6d34251a4c579f9b0eb7a50291d808ed.png)
.
%V0
Neka su $a$, $b$, $c$, $d$ realni brojevi takvi da vrijede jednakosti $$$
\begin{gather*}
2\cos a + 6 \cos b +7 \cos c+ 9 \cos d=0, \\
2\sin a-6\sin b +7\sin c -9\sin d=0.
\end{gather*}
$$$ Ako je $\cos(b+c)\neq 0$, odredi vrijednost izraza $\displaystyle \frac{\cos(a+d)}{\cos(b+c)}$.