how to locate(geographical location) a person with the mobile number?
Get a court order.
It is possible to locate a mobile phone to within 50m or so (in a good signal area) from signal strength information gathered when the mobile transmits it's regular 'keeping in touch' signals. The security services will have access to this information if they need it so they can monitor the movements of crime suspects etc. Also, there are commercial companies who provide tracking information for a subscription fee, which must be with the permission of the trackee (at least in the UK). But for someone to track a mobile phone of their choice at will, no chance.
Legally you probably can't as you would need to have access to the Cell providers network controllers to find out which cell mast the call was routed from.There are ways to allow people to access your position from your phone but it has to be done voluntarily by the phone user. - Google provide this feature for phones etc equipped with GPS units.
It's impossible. You can't. Don't even try. There is no way on earth you could do that.