using lo cual
why do one use lo cual or the combination of lo/la/los/las with cual?
5 Answers
Mi tía, la que es profesora, viene a visitarme hoy día.
My aunt, the one who is a professor, is coming to visit me today.
Las mesas, las que son de plástico, son baratas.
The tables, the ones that are made of plastic, are cheap.
Mi tío, el que es taxista, llegará pronto.
My uncle, the one who is a taxi driver, will arrive soon.
Mis pantalones, los que son viejos, son muy cómodos.
My pants, the ones that are old, are very comfortable.
Another set of relative pronouns can be used in place of el que, la que, los que, and las que:
el cual
la cual
los cuales
las cuales
El cual, la cual, los/las cuales translates to 'which'.
El camino del cual hablamos esta en el centro del pais ... The road (which) we're talking about is in the middle of the country.
Tengo dos libros favoritos, de los cuales, el mas antiguo es el mas interesante ... I have two favorite books, of which one is much more interesting.
Espero que esto le haya ayudado 
'Lo cual' is a relative pronoun.
First let's summarize. A pronoun is a word that takes the place of another word so you don't have to keep saying it over and over. The relative part just means it's relating back to something/an idea that you've mentioned already. Kind of confusing with just this little text explanation, but that's what examples are for, right?
Joe Satriani fue el que enseñó a Steve Vai, lo cual significa que cada vez que toque, se oye un poco de Satriani.
That means: Joe Satriani was the one who taught Steve Vai, which means that every time he plays, you can hear a little bit of Satriani.
There's actually 2 relative pronouns there. 1) el que 2) lo cual
'El que' is relating back to Joe Satriani, There also exists 'la que' but we use 'el que' here because Satriani is a guy. He was 'the one' who taught Steve Vai.
The 'lo cual' is relating back, making reference to the whole entire idea of Steve Vai being taught by Satriani. That whole idea doesn't have a gender, it's a general idea, so no el or la this time, you go with the neuter 'lo'. Lo cual, which.
Hopefully that helped.
-Charlius-
Well, I'm not exactly sure if I'm right, but isn't lo/la/los/las used instead of the object/noun? Cual is which, so I'm guessing it's something like "In which she/he" or something like that. Where did you get this? Is it like from a homework assignment? 
