Evaluate 
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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Generated by AI. May contain inaccuracies — always verify with your textbook.
