|x+1| + |x+2| + | x-1|= 20

Please tell me how to generate equations for below -

1) |x+1| + |x+2| + | x-1|= 20
2) |x+1| - |x+2| - | x-1|= 20

I know check points would be -1 -2 and +1 . but then how to proceed with equations ?

for x <= -2
for -2 <= x <= -1
for -1 <= x <= +1
for x >= +1

I have spend more than twelve hours and checked almost every resource online but couldn't find reasoning behind +ve and -ve signs for the test cases [ brackets ].


PLEASE HElp !
Regards,
Sandip66612