[prog] using a -ln option with GCC when compiling c code with math.h

[Guru -]

Hi.
I'm just wondering (this problem caused me a lot of trouble during Uni until 
I figured it out),
why is it necessary to use the -ln flag with GCC when compiling something 
that uses math.h?
(this problem forced me to go back to Borland C until I figured it out).

Thanks

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