$1.a)A=\sqrt{(2+\sqrt{5})^2}+\sqrt{(2-\sqrt{5})^2}$
$A=2+\sqrt{5}+\sqrt{5}-2$
$A=2\sqrt{5}$
$b)B=\sqrt{45}+\sqrt{20}-\sqrt{5}$
$B=3\sqrt{5}+2\sqrt{5}-\sqrt{5}$
$B=4\sqrt{5}$
$c)C=\dfrac{1}{2}\sqrt{20}-\sqrt{80}+\dfrac{2}{3}\sqrt{45}$
$C=\dfrac{1}{2}.2\sqrt{5}-4\sqrt{5}+\dfrac{2}{3}.3\sqrt{5}$
$C=\sqrt{5}-4\sqrt{5}+2\sqrt{5}$
$C=-\sqrt{5}$
$2.a)A=\sqrt{50}.\sqrt{\dfrac{5}{49a}}+\sqrt{9a^2}(a>0)$
$A=5\sqrt{2}.\dfrac{\sqrt{5}}{7\sqrt{a}}+3a$
$A=\dfrac{5\sqrt{10}}{7\sqrt{a}}+3a$
$A=\dfrac{5\sqrt{10}}{7\sqrt{a}}+\dfrac{21a\sqrt{a}}{7\sqrt{a}}$
$A=\dfrac{5\sqrt{10}+21a\sqrt{a}}{7\sqrt{a}}$
$b)B=\dfrac{\sqrt{45}}{\sqrt{5}}+\sqrt{(1-\sqrt{5})^2}$
$B=\dfrac{\sqrt{5}.\sqrt{9}}{\sqrt{5}}+\sqrt{5}-1$
$B=\sqrt{9}+\sqrt{5}-1$
$B=3+\sqrt{5}-1$
$B=2+\sqrt{5}$
