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सिद्ध कीजिए - `2tan^(-1)((1)/(2))+tan^(-1)((1)/(7))=tan^(-1)((31)/(17)).`

Answer» L.H.S. `=2tan^(-1)((1)/(2))+tan^(-1)((1)/(7))`
`=tan^(-1).((2xx(1)/(2))/(1-((1)/(2))^(2)))+tan^(-1)((1)/(7)),`
`[because 2tan^(-1)x=tan^(-1)((2x)/(1-x^(2)))]`
`=tan^(-1)((4)/(3))+tan^(-1)((1)/(7))`
`=tan^(-1)(((4)/(3)+(1)/(7))/(1-(4)/(3)xx(1)/(7)))`
`=tan^(-1)(((28+3)/(21))/((21-4)/(21)))`
`=tan^(-1).(31)/(17)`
= R.H.S.


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