Q.Calculate the gravitational field at point O due to three masses $m_1$, $m_2$ and $m_3$ whose positions are given by the following figure [figure: three masses m1, m2 and m3 arranged around an origin point O with side markings labelled 'a', with axes x and y drawn; the exact placement of each mass relative to O is shown only in the diagram, not stated in the running text]. If the masses $m_1$ and $m_2$ are equal, what is the change in gravitational field at the point O?