How does the force of gravitation between two objects change when the distance between them is reduced to half?

Explanation

The force of gravitional between two objects is `F=G (m_1m_2)/(d^2)`
If the distance is reduced to half `d.=d/2`
`F.=G (m_1m_2)/((d.)^(2))=G (m_1m_2)/((d//2)^(2))=4G (m_1m_2)/(d^2)=4F`
The force of gravition between two objects become 4 times the original force.