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Evaluate : \(\begin{vmatrix}cos\,15° & \ sin\,15° \\[0.3em]sin\,75° & cos\,75° \\[0.3em]\end{vmatrix}\)

Answer»

Expanding the determinant, we get

cos 15°. cos 75° – sin 15°. sin 75° 

= cos (15° + 75°) 

= cos 90° = 0

[Note: cos (A + B) = cos A. cos B – sin A. sin B]



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