CBSE Notes, Lectures

CBSE - Mathematics - Introduction to Trigonometry

Introduction to Trigonometry

NCERT Exercise Excercise 8.4

Evaluate :
(i) (sin263° + sin227°)/(cos217° + cos273°)
(ii)  sin 25° cos 65° + cos 25° sin 65°

(i) (sin263° + sin227°)/(cos217° + cos273°)
   = [sin2(90°-27°) + sin227°]/[cos2(90°-73°) + cos273°)]
   = (cos227° + sin227°)/(sin227° + cos273°)
   = 1/1 =1                       (��� sin2A + cos2A = 1)

(ii) sin 25° cos 65° + cos 25° sin 65°
   = sin(90°-25°) cos 65° + cos(90°-65°) sin 65°
   = cos 65° cos 65° + sin 65° sin 65°
   = cos265° + sin265° = 1

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