Q18 of 90 Page 8

Given,



Now,




Now,



Now,




Now,


xy + yz + xz






{∵ cos (A + B) = cos A cos B – sin A sin B}







{sin (180° - A) = sin A ; sin (180° + A) = -sin A;


cos (180° - A) = -cos A & cos (180° + A) = -cos A }







= 0


= R.H.S.


Hence Proved


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