Reflect a triangle

A reflection moves every corner of a shape, but it never changes the shape's size. You will reflect a triangle and check that its area stays the same.

The idea. In the x-axis $(x, y) \to (x, -y)$; in the y-axis $(x, y) \to (-x, y)$; in the origin $(x, y) \to (-x, -y)$. The area of a triangle is $\tfrac{1}{2}|x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2)|$.

Your tasks.

1. In reflect, return the image of p in the mirror "x", "y" or "o".
2. Fill image with the three corners of triangle reflected in the y-axis.
3. Set same_area to True if area(triangle) equals area(image).