Question

If sin 0 = - and e lies in IIIrd quadrant then the value of cos (b) v

Defence Exams

Maths

Solution

125

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( sin theta=-frac{4}{5} ) ( cos theta=-frac{3}{5} ) ( cos 2 theta=2 cos ^{2} theta-1 ) ( Rightarrow cos theta=2 cos ^{2} frac{theta}{2}-1 ) ( Rightarrow cos ^{2} frac{theta}{2}=-frac{cos theta+1}{frac{2}{frac{3}{2}}-frac{1}{sqrt{5}}} ) ( =-sqrt{-frac{3}{2}} )