Python can't define tuples in a function
Tuple parameters are no longer supported in Python3: http://www.python.org/dev/peps/pep-3113/
You may unpack your tuple at the beginning of your function:
def add_vectors(v1, v2):
angle_1, l_1 = v1
angle_2, l_2 = v2
x=math.sin(angle1)*l_1+math.sin(angle2)*l_2
y=math.cos(angle1)*l_1+math.cos(angle2)*l_2
angle=0.5*math.pi-math.atan2(y, x)
length=math.hypot(x, y)
return (angle, length)