Describe two vectors a and b such that a overscript right-arrow endscripts plus b overscript right-arrow endscripts equals c overscript right-arrow endscripts and a plus b equals c

Define the two vectors as


Then if vector c is defined by

then


Example:
If

then

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts