BT: giải các pt sau
1. \(\frac{x+1}{2013}+\frac{x+2}{2012}=\frac{x+3}{2011}+\frac{x+4}{2010}\)
2. \(\frac{3x+2}{4}+\frac{x+3}{2}=\frac{x-1}{3}-\frac{-x-1}{12}\)
3.\(\frac{x+1}{x-1}-\frac{x-1}{x+1}+\frac{x^2+3}{1-x^2}=0\)
4. \(\frac{1}{x+2}-\frac{3x}{x-2}=\frac{16}{x^2-4}\)