diff --git a/pymath/polynomDeg2.py b/pymath/polynomDeg2.py
index d17c762..793acd5 100644
--- a/pymath/polynomDeg2.py
+++ b/pymath/polynomDeg2.py
@@ -10,11 +10,15 @@ from math import sqrt
 class Polynom_deg2(Polynom):
 
     """ Degree 2 polynoms
-    Child of Polynom with some extro tools
+    Child of Polynom with some extra tools
     """
 
     def __init__(self, coefs = [0, 0, 1], letter = "x"):
         """@todo: to be defined1. """
+        if len(coefs) < 3 or len(coefs) > 4:
+            raise ValueError("Polynom_deg2 have to be degree 2 polynoms, they need 3 coefficients, {} are given".format(len(coefs)))
+        if coefs[2] == 0:
+            raise ValueError("Polynom_deg2 have to be degree 2 polynoms, coefficient of x^2 can't be 0")
         Polynom.__init__(self, coefs, letter)
 
     @property
@@ -34,27 +38,101 @@ class Polynom_deg2(Polynom):
         """Compute the discriminant expression
         :returns: discriminant expression
 
+        >>> P = Polynom_deg2([1,2,3])
+        >>> P.delta
+        < Expression [2, 2, '^', 4, 3, 1, '*', '*', '-']>
+        >>> for i in P.delta.simplify():
+            print(i)
+        2^{  2 } - 4 \times 3 \times 1
+        4 - 4 \times 3
+        4 - 12
+        -8
+        >>> P.delta.simplified()
+        -8
         """
+
         return Expression([self.b, 2, op.pw, 4, self.a, self.c, op.mul, op.mul, op.sub])
 
     def roots(self):
-        """Compute roots of the polynom
+        """ Compute roots of the polynom
+
+        /!\ Can't manage exact solution because of pymath does not handle sqare root yet
+
+        # TODO: Pymath has to know how to compute with sqare root |mar. févr. 24 18:40:04 CET 2015
+
+        >>> P = Polynom_deg2([1, 1, 1])
+        >>> P.roots()
+        []
+        >>> P = Polynom_deg2([1, 2, 1])
+        >>> P.roots()
+        [-1.0]
+        >>> P = Polynom_deg2([-1, 0, 1])
+        >>> P.roots()
+        [-1.0, 1.0]
         """
-        if self.delta > 0:
-            roots = [(-self.b - sqrt(self.delta)
+        if self.delta.simplified() > 0:
+            self.roots = [(-self.b - sqrt(self.delta.simplified()))/(2*self.a), (-self.b + sqrt(self.delta.simplified()))/(2*self.a)]
+        elif self.delta.simplified() == 0:
+            self.roots = [-self.b /(2*self.a)]
+        else:
+            self.roots = []
+        return self.roots
+
+    def tbl_sgn(self):
+        """ Return the sign line for tkzTabLine
+
+        >>> P = Polynom_deg2([2, 5, 2])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, +, z, -, z , +,}'
+        >>> P = Polynom_deg2([2, 1, -2])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, -, z, +, z , -,}'
+        >>> P = Polynom_deg2([1, 2, 1])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, +, z, +,}'
+        >>> P = Polynom_deg2([0, 0, -2])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, -, z, -,}'
+        >>> P = Polynom_deg2([1, 0, 1])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, +,}'
+        >>> P = Polynom_deg2([-1, 0, -1])
+        >>> P.tbl_sgn()
+        '\\tkzTabLine{, -,}'
+        """
+        if self.delta.simplified() > 0:
+            if self.a > 0:
+                return "\\tkzTabLine{, +, z, -, z , +,}"
+            else:
+                return "\\tkzTabLine{, -, z, +, z , -,}"
+        elif self.delta.simplified() == 0:
+            if self.a > 0:
+                return "\\tkzTabLine{, +, z, +,}"
+            else:
+                return "\\tkzTabLine{, -, z, -,}"
+        else:
+            if self.a > 0:
+                return "\\tkzTabLine{, +,}"
+            else:
+                return "\\tkzTabLine{, -,}"
+
+    
 
 
 
 
 if __name__ == '__main__':
-    from .render import txt
-    with Expression.tmp_render(txt):
-        P = Polynom_deg2([2, 3, 4])
-        print(P)
+   # from .render import txt
+   # with Expression.tmp_render(txt):
+   #     P = Polynom_deg2([2, 3, 4])
+   #     print(P)
 
-        print("Delta")
-        for i in P.delta.simplify():
-            print(i)
+   #     print("Delta")
+   #     for i in P.delta.simplify():
+   #         print(i)
+
+    import doctest
+    doctest.testmod()