#get the polygon
sC = arcpy.SearchCursor(polygon)
for row in sC:
    polygonshape = row.Shape
del sC

#creation of the polyline(s):

feature_info = [[[p1.x, p1.y], [x, y]], [[p2.x, p2.y], [x, y]], [[p3.x, p3.y], [x, y]]]
features = []
for feature in feature_info:
    array = arcpy.Array()
    for point in feature:
        P = arcpy.Point()
        P.X = point[0]
        P.Y = point[1]
        array.add(P)
        features.append(arcpy.Polyline(array))

#the actual check:
for item in features:
    in_poly = polygonshape.contains(item) #this is always false