(CBSE 2011)Answer :
Let Δ = 
By expanding the determinant about the first row.
Δ = cos 15° cos 75° - sin 75° sin 15°
We know that:
cos(A + B) = cos A cos B – sin A sin B
∴ Δ = cos (75 + 15)° = cos 90° = 0
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