माना ` sec^(-1)""(5sqrt(2))/(7)=theta`
`implies sec theta=(5sqrt(7))/(7)`
इसलिए `cos theta=(7)/(5sqrt(2))`
तथा ` tan theta=(1)/(7)" " :. theta=tan^(-1)""(1)/(7)`
माना बायाँ पक्ष `=2(tan^(-1)""(1)/(5)+tan^(-1)""(1)/(8))+tan^(-1)""(1)/(7)`
`=2 tan^(-1)""[(((1)/(5)+(1)/(8)))/(1-(1)/(5)xx(1)/(8))]+tan^(-1)""(1)/(7)`
`2tan^(-1)""[(13)/(40)xx(40)/(39)]+tan^(-1)""(1)/(7)`
`= 2 tan^(-1)""(1)/(3) +tan^(-1)""(1)/(7)`
`tan^(-1)[(2xx(1)/(3))/(1-((1)/(3))^(2))]+tan^(-1)""(1)/(7)`
`tan^(-1)""(3)/(4)+tan^(-1)""(1)/(7)`
`tan^(-1)""(((3)/(4)+(1)/(7)))/((1-(3)/(4)xx(1)/(7)))`
`= tan^(-1)""(25)/(25)=1=(pi)/(4)=` दायाँ पक्ष
