1.

`cos^(- 1)sqrt((sqrt(1+x^2)+1)/(2sqrt(1+x^2)))`

Answer» `cos^(-1)sqrt(((1+x^2)+1)/(2sqrt(1+x^2))`
Let `x=tantheta`
`1+x^2=1+tan^2theta=secc^2theta`
`=cos^(-1)sqrt((sqrt(sec^2theta)+1)/(2sqrtsec^2theta))`
`=cos^(-1)sqrt((sectheta+1)/(2sectheta))`
`=cos^(-1)sqrt((1+costheta)/2)`
`cos2theta=2cos^2theta-1`
`1+cos2theta=2cos^2theta`
`1+costheta=2cos^2(theta/2)`
`cos^(-1)sqrt(1/2(2cos^2(theta/2)))`
`cos^(-1)sqrt(cos^2(theta/2))`
`cos^(-1)(cos(theta/2))`
`theta/2`
`1/2tan^(-1)x`.


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