a) $\sqrt{8-2√15}$ + $\sqrt{4-2√3}$
= $\sqrt{(√5-√3)²}$ + $\sqrt{(√3-1)²}$
`= |√5-√3| + |√3-1|`
`= √5 - √3+√3-1=√5-1`
b) $\dfrac{4}{√7-√3}$ + $\dfrac{6}{3+√3}$ + $\dfrac{√7-7}{√7-1}$
=$\dfrac{4(√7+√3)}{(√7-√3)(√7+√3)}$ + $\dfrac{6(3-√3)}{(3+√3)(3-√3)}$+$\dfrac{√7(1-√7)}{√7-1}$
= $\dfrac{4(√7+√3}{7-3}$ + $\dfrac{6(3-√3}{9-3}$ + $\dfrac{-√7(√7-1)}{√7-1}$
= $\dfrac{4(√7+√3)}{4}$ + $\dfrac{6(3-√3)}{6}$ - √7
`= √7+√3+3-√3 - √7 = 3`
