Résoudre :
1
\(\arctan 2x + \arctan 3x = \frac \pi4\).
2
\(\arctan\left(\frac{x-1}{x-2}\right) + \arctan\left(\frac{x+1}{x+2}\right) = \frac\pi4\).
3
\(\arctan\left(\frac1x\right) + \arctan\left(\frac{x-1}{x+1}\right) = \frac\pi4\).
4
\(\arctan(x-3) + \arctan(x) + \arctan(x+3) = \frac {5\pi}4\).