`a)\sqrt{\frac{a}{b}}+\sqrt{ab}+\frac{a}{b}\sqrt{\frac{b}{a}}`
`=\sqrt{\frac{a}{b}}+\sqrt{ab}+\sqrt{\frac{a^2}{b^2}\frac{b}{a}}`
`=\sqrt{\frac{a}{b}}+\sqrt{ab}+\sqrt{\frac{a}{b}}`
`=\sqrt{ab}+2\sqrt{\frac{a}{b}}`
`b)\sqrt{\frac{m}{1-2x+x^2}}.\sqrt{\frac{4m-8mx+4mx^2}{81}}`
`=\sqrt{\frac{m}{(x-1)^2}}.\sqrt{\frac{4m(x-1)^2}{81}}`
`=\sqrt{\frac{m.4m(x-1)^2}{81.(x-1)^2}}`
`=\sqrt{\frac{4m^2}{81}}`
`=\frac{2m}{9}` `(m>0)`