\(a,=2\sqrt{5}-9\sqrt{5}+3\sqrt{5}-\sqrt{5}=-5\sqrt{5}\\ b,=\sqrt{14-2\sqrt{45}}-\left|\sqrt{5}-5\right|=\sqrt{9-2\sqrt{9}.\sqrt{5}+5}-5+\sqrt{5}=\sqrt{\left(3-\sqrt{5}\right)^2}-5+\sqrt{5}=3-\sqrt{5}-5+\sqrt{5}=-2\)
\(c,=\left(\dfrac{-\sqrt{7}\left(\sqrt{2}-1\right)}{\sqrt{2}-1}-\dfrac{\sqrt{5}\left(\sqrt{3}-1\right)}{\sqrt{3}-1}\right).\left(\sqrt{7}-\sqrt{5}\right)=\left(-\sqrt{7}-\sqrt{5}\right)\left(\sqrt{7}-\sqrt{5}\right)=-\left[\left(\sqrt{7}+\sqrt{5}\right)\left(\sqrt{7}-\sqrt{5}\right)\right]=-2\)
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