a) thực hiện phép tính sau:
+) \(\sqrt{125}-2\sqrt{20}-3\sqrt{80}+4\sqrt{45}\)
+) \(\sqrt{\left(1-2\sqrt{7}\right)^2}+\sqrt{8+2\sqrt{7}}\)
+) \(\sqrt{12}-4\sqrt{75}-3\sqrt{27}+5\sqrt{48}\)
+) \(\dfrac{1}{1-\sqrt{3}}-\dfrac{1}{1+\sqrt{3}}\)
b) tìm đk để căn sau có nghĩa :
\(\sqrt{\dfrac{2}{5-x}}\)
c) giải pt sau:
+) \(\sqrt{4x+1}=5\)
Bài 1:
a: \(\sqrt{125}-2\sqrt{20}-3\sqrt{80}+4\sqrt{45}\)
\(=5\sqrt{5}-4\sqrt{5}-12\sqrt{5}+12\sqrt{5}=\sqrt{5}\)
b: \(\sqrt{\left(1-2\sqrt{7}\right)^2}+\sqrt{8+2\sqrt{7}}\)
\(=2\sqrt{7}-1+\sqrt{7}+1=3\sqrt{7}\)
c:\(\dfrac{1}{1-\sqrt{3}}-\dfrac{1}{1+\sqrt{3}}\)
\(=\dfrac{1+\sqrt{3}-1+\sqrt{3}}{-2}=-\dfrac{2\sqrt{3}}{2}=-\sqrt{3}\)
