Đáp án:
$a)2\sqrt{7}\\ b)2\sqrt{11}-1.$
Giải thích các bước giải:
$a)\sqrt{\left(\sqrt{7}-\sqrt{2}\right)^2}+\sqrt{\left(\sqrt{7}+\sqrt{2}\right)^2}\\ =|\sqrt{7}-\sqrt{2}|+|\sqrt{7}+\sqrt{2}|\\ =\sqrt{7}-\sqrt{2}+\sqrt{7}+\sqrt{2}\\ =2\sqrt{7}\\ b)\sqrt{\left(\sqrt{11}+4\right)^2}-\sqrt{\left(\sqrt{11}-5\right)^2}\\ =|\sqrt{11}+4|-|\sqrt{11}-5|\\ =\sqrt{11}+4-\left(5-\sqrt{11}\right)\\ =\sqrt{11}+4-5+\sqrt{11}\\ =2\sqrt{11}-1.$
