c: Ta có: \(\sqrt{\left(\sqrt{7}-4\right)^2}\cdot\sqrt{23+4\sqrt{28}}\)
\(=\left(4-\sqrt{7}\right)\left(4+\sqrt{7}\right)\)
=16-7
=9
d: Ta có: \(\dfrac{5-\sqrt{15}}{\sqrt{5}-\sqrt{3}}-\dfrac{2\sqrt{5}-6}{\sqrt{14-2\sqrt{45}}}\)
\(=\sqrt{5}-\dfrac{6-2\sqrt{5}}{3-\sqrt{5}}\)
\(=\sqrt{5}-2\)
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