Simplfy[tex] \sqrt{20} \times \sqrt{3} \times \sqrt{18} [/tex]A[tex]5 \sqrt{30} [/tex]B[tex]5 \sqrt{10} [/tex]C[tex]6 \sqrt{30} [/tex]D[tex]6 \sqrt{10} [/tex]-----------------------------------------------------------------------Simplify[tex]5 \sqrt{7} + \sqrt{7} - 2 \sqrt{7} [/tex]A[tex]4 \sqrt{21} [/tex]B[tex]3 \sqrt{21} [/tex]C[tex]4 \sqrt{7} [/tex]D[tex]3 \sqrt{7} [/tex]​

Answer:[tex]\large\boxed{C.\ 6\sqrt{30}}\\\boxed{C.\ 4\sqrt7}[/tex]Step-by-step explanation:[tex]\text{Use}\ \sqrt{ab}=\sqrt{a}\cdot\sqrt{b} \\\\\sqrt{20} \times \sqrt{3} \times \sqrt{18}=\sqrt{20\times3\times18}=\sqrt{4\times5\times3\times3\times6}\\\\=\sqrt4\times\sqrt9\times\sqrt{5\times6}=2\times3\times\sqrt{30}=\boxed{6\sqrt{30}}\\==============================\\\\5 \sqrt{7} + \sqrt{7} - 2 \sqrt{7}=5 \sqrt{7} + 1\sqrt{7} - 2 \sqrt{7}=(5+1-2)\sqrt7=\boxed{4\sqrt7}[/tex]