st: interaction between two continuous variables

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Hi,

I have the following model y continuous , x1 x2 continuous

I do a regression  with

reg y cx1 cx2 cx1*cx2

with
cx1= x1 -mean (x1)
cx2= x2 -mean (x2)

both the paramters of cx1 and cx2 are signficants , which mean that the 
slope of x2 is signficant for x1=mean (x1)

the paramter of cx1*cx2 is also signficant

How to interpret the parameter of cx1*cx2 ?

My first interpretation is that  there are at least two values of x1 , where 
the slopes of x2 are not parallels

but how to know, that the slope of x2 for a given value of x1=a is 
signficant?

like using a lincom command

Any comments, please

Thanks

Sami

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