Let 0 < α < π , 0 < β < π and cos α + cos β − cos ( α + β ) = 3 2 . Then the relation between α and β will be

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α > β α < β α = β 3 Solution: We have, cos ‌ α + cos ‌ β − cos ( α + β ) = 3 2 It is possible when cos ‌ α = cos ‌ β = − cos ( α + β ) = 1 2 ∴ α = 60 ° , β = 60 ° and α + β = 120 ° ∴ α = β" >