the problem about the geometry

Dear all.

I input the command below:

UPDATE iphone_en SET location = GeometryFromText(cast(POINT('||cast(latitude as varchar(10))||', '||cast(longitude as varchar(10))||') as geometry),-1);
ERROR : invalid input syntax for type double precision: "||cast(latitude as varchar(10))||"

DB has some fields(name, id, ----, latitude, longitude, ----, location).

I made the field of location using by addgeometrycolumn.

I want to input the value(latitude, longitude) to location.

How can I input the right command?

Best regards and thanks in advance
Kevin.