How do the same random value in second coordinate in line in QGIS

It is my first tag here, I don't know how to create a random() ... to make the same two coordinates with B and B1

For example

first line in virtual layer - A,B,

second line in virtual layer - B1,C

I want do something in python but i don't know what. I tried random.uniform and random.setstate, but I don't know how I can do that B and B1 have the same coordinate ?

Help me :)

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