def __str__(self):
        return "\n".join([str(x) for x in self])
def getAp3(self):
        ret = math.acos(((self.getLenp1() * self.getLenp1() + self.getLenp2() * self.getLenp2()) - self.getLenp3() * self.getLenp3()) / (2* self.getLenp1() * self.getLenp2()))
        return ret