Đáp án:
$1)2\sqrt{5}+15\sqrt{2}-18\\ 2)A=45(c-1)\\ 3)\sqrt{17}-\sqrt{2}\\ 4)60\sqrt{2}-80$
Giải thích các bước giải:
$1)2\sqrt{5}+3\sqrt{50}-3\sqrt{36}\\ =2\sqrt{5}+3\sqrt{25.2}-3.6\\ =2\sqrt{5}+15\sqrt{2}-18\\ 2)A=\sqrt{45.15(c-1)^2.3}(c>1)\\ =\sqrt{45^2(c-1)^2}\\ =45|c-1|\\ =45(c-1)\\ 3)\sqrt{19-2\sqrt{34}}\\ =\sqrt{17-2\sqrt{17}.\sqrt{2}+2}\\ =\sqrt{(\sqrt{17}-\sqrt{2})^2}\\ =\sqrt{17}-\sqrt{2}\\ 4)(3\sqrt{16}+2\sqrt{81}-4\sqrt{50}).2\sqrt{2}\\ =(3.4+2.9-4\sqrt{25.2}).2\sqrt{2}\\ =(12+18-20\sqrt{2}).2\sqrt{2}\\ =(30-20\sqrt{2}).2\sqrt{2}\\ =60\sqrt{2}-80$