It is known that a focal point of an ellipse is f (1,1), the corresponding collimator is x + y-4 = 0, and the eccentricity is √ 2 / 2

It is known that a focal point of an ellipse is f (1,1), the corresponding collimator is x + y-4 = 0, and the eccentricity is √ 2 / 2

Using the definition method!
The distance to the focus is greater than the distance to the guide line = eccentricity
Just list it and simplify it!