1,$(√7-√3)^{2}$+$\sqrt{84}$
= 7+3-2$\sqrt{21}$ + 2$\sqrt{21}$
= 7+3
= 10
2,(15$\sqrt{200}$-3$\sqrt{400}$+2$\sqrt{50}$):$\sqrt{10}$
= (150$\sqrt{2}$-45$\sqrt{2}$+10$\sqrt{2}$):$\sqrt{10}$
=$\dfrac{115\sqrt{5}}{5}$
3,$\sqrt{9-4\sqrt{5} }$ - $\sqrt{5}$
= $\sqrt{5-4\sqrt{5}+4}$ - $\sqrt{5}$
=$\sqrt{(\sqrt{5} -2)^2}$ - $\sqrt{5}$
=|$\sqrt{5}$ -2|- $\sqrt{5}$
=$\sqrt{5}$ -2- $\sqrt{5}$
=-2
Chúc bạn học tốt !!
@Katniss