[m]f`(x)=\frac{1}{(x-1)ln3}\cdot (x-1)`[/m]
[m]f`(x)=\frac{1}{(x-1)ln3}[/m]
ii)
[m]f`(x)=2\cdot (3^{x}+3^{-x})\cdot (3^{x}+3^{-x})`[/m]
[m]f`(x)=2\cdot (3^{x}+3^{-x})\cdot (3^{x}ln3\cdot x`+3^{-x}\cdot ln3\cdot (-x)`)[/m]
[m]f`(x)=2\cdot (3^{x}+3^{-x})\cdot (3^{x}ln3+3^{-x}\cdot ln3\cdot (-1))[/m]
[m]f`(x)=2\cdot (3^{x}+3^{-x})\cdot (3^{x}-3^{-x})\cdot ln3[/m]
[m]f`(x)=2\cdot \cdot (3^{2x}-3^{-2x})\cdot ln3[/m]