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सिद्ध कीजिए कि ` tan^(-1)""(1)/(2)+tan^(-1)""(1)/(5)+tan^(-1)""(1)/(8)=(pi)/(4)`

Answer» `tan^(-1)x +tan^(-1)y+tan^(-1)z=tan^(-1)""(x+y+x-xyz)/(1-xy-yz-zx)`
`tan^(-1)""((1)/(2)+(1)/(5)+(1)/(8)-(1)/(2)xx(1)/(5)xx(1)/(8))/(1-(1)/(2)xx(1)/(5)-(1)/(5)xx(1)/(8)-(1)/(8)xx(1)/(2))`
` =tan^(-1)""((40+16+10-1)/(80))/((80-8-2-5)/(80))`
` =tan^(-1)""((65)/(65))=(pi)/(4)`


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