Q1 of 44 Page 4

Evaluate:

(CBSE 2011)

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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