Question

mọi người hướng dẫn mình làm bài này zới

 

Answer 1

\(a,7+4\sqrt{3}\\ =7+2.2\sqrt{3}\\ =2^2+2.2\sqrt{3}+\sqrt{3^2}\\ =\left(2+\sqrt{3}\right)^2\\ b,6-2\sqrt{5}\\ =\sqrt{5^2}-2.\sqrt{5}.1+1^2\\ =\left(\sqrt{5}-1\right)^2\\ c,\left(5-\sqrt{2}\right)^2\\ =5^2-2.5.\sqrt{2}+\sqrt{2^2}\\ =25-10\sqrt{2}+2\\ =27-10\sqrt{2}\\ d,\sqrt{9+4\sqrt{5}}-\sqrt{9-4\sqrt{5}}\\ =\sqrt{9+2.2\sqrt{5}}-\sqrt{9-2.2\sqrt{5}}\\ =\sqrt{\sqrt{5^2}+2.2\sqrt{5}+2^2}-\sqrt{\sqrt{5^2}-2.2\sqrt{5}+2^2}\\ =\sqrt{\left(\sqrt{5}+2\right)^2}-\sqrt{\left(\sqrt{5}-2\right)^2}\\ =\left(\sqrt{5}+2\right)-\left(\sqrt{5}-2\right)\\ =\sqrt{5}+2-\sqrt{5}+2\\ =4\)