Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given an array of points on the X-Y plane points where points[i] = [xi, yi]. The points form a polygon when joined sequentially.
Return true if this polygon is convex and false otherwise.
You may assume the polygon formed by given points is always a simple polygon. In other words, we ensure that exactly two edges intersect at each vertex and that edges otherwise don't intersect each other.
 
Please complete the following python code precisely:
```python
class Solution:
    def isConvex(self, points: List[List[int]]) -> bool:
```