1.

`tan^(-1)""((sqrt(1-cosx))/(1+cosx)),0ltxltpi`

Answer» `tan^(-1)(sqrt((1-cosx)/(1+cosx)))`
`=tan^(-1)(sqrt((2sin^(2)""(x)/(2))/(2cos^(2)""(x)/(2))))=tan^(-1)((sin""(x)/(2))/(cos""(x)/(2)))`
`=tan^(-1)(tan""(x)/(2))=(x)/(2)`


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