Giải các pt sau:
1.$\sqrt{x^{2}+5}+5=3x+\sqrt{x^{2}+15}$
2.$x^{3}-3x^{2}-8x+40=4\sqrt[4]{4x+4}$
3.$2x^{2}-11x+21=3\sqrt[3]{4x-4}$
4.$\sqrt{x^{2}+x-1}+\sqrt{-x^{2}+x+1}=x^{2}-x+2$
5.$\sqrt{2x+4}-2\sqrt{2-x}=\frac{6x-4}{\sqrt{x^{2}+4}}$
6.$(\sqrt{x+3}-\sqrt{x+1})(x^{2}+\sqrt{x^{2}+4x+3})=2x$
7.$2x+1+x\sqrt{x^{2}+2}+(x+1)\sqrt{x^{2}+2x+3}=0$