1.$\sqrt{x1-1^2}+2\sqrt{x2-2^2}+3\sqrt{x3-3^2}+....+2013\sqrt{x2013-2013^2}=\frac{1}{2}(x1+x2+....+x2013)$
2.$\sqrt{x-1}+\sqrt{3-x}+x^2+2x-3-\sqrt{2}=0$
3.$x\sqrt{y-1}+y\sqrt{x-1}=xy$
4.$\sqrt{2-x^2}+\sqrt{2-\frac{1}{x^2}}=4-(x+\frac{1}{x})$(cái này mình ko chắc cái (x+\frac{1}{x}) đúng )
5.$\sqrt{4x-1}+\sqrt{4x^2-1}=1$
6.$13\sqrt{x^2-x^4}+9\sqrt{x^2+x^4}=16$
7.$x\sqrt{y-1}+2y\sqrt{x-1}=\frac{3}{2}xy$