The value of the determinant $Δ=\begin{vmatrix}\cos (α+β)&- \sin (α+β)& \cos 2β\\\sin α&\cos α&\sin β\\-\cos α&\sin α&-\cos β\end{vmatrix}$, is
Answer & explanation
Correct answer: option 4
Applying $R_1 → R_1 + (\sin β) R_2 + (\cos βB) R_3$, we get
$Δ=\begin{vmatrix}0&0&0\\\sin α&\cos α&\sin β\\-\cos α&\sin α&-\cos β\end{vmatrix}=0$