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Evaluate \( \begin{bmatrix} cos 65 ^\circ & sin 65^\circ\\[0.3em] sin 25^\circ & cos 25^\circ\\[0.3em] \end{bmatrix}\). Evaluate |(cos 65° sin 65°)(sin25°, cos 25°)| |
Answer» By directly opening this determinant cos65° × cos25° -sin25° × sin65° = cos(65°+25°) ∵ cosAcosB - sinAsinB = cos(A+B) = cos90° = 0 ∵ cosAcosB - sinAsinB = cos(A+B) |
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