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Solution


Q.

The value of (sin 70°) (cot 10° cot 70° – 1) is           [2025]
1 0  
2 1  
3 3/2  
4 2/3  

Ans.

(2)

We have, 

sin 70°(cos 10°cos70°–sin 10°sin 70°sin 10° sin 70°)

=sin 70°[cos 80°sin 10° sin 70°]          [∵ cos (A + B) = cos A cos B – sin A sin B]

=cos 80°cos 80°=1        [∵ sin(90°–θ)=cos θ]