this is just a hint for this qustion

two opp points are given

find the equation of the diagonal line

......NOW find the slopes of the lines by using

tanz =(m1-m2)/(1+m1m2)

M1 is the slope of diagonal line and M2 is the slope of the line passing through any of the point

value ofz is 45 degrees asit is a square

getting slopes fin the equations passin through first pt and nother passing through 2nd point

after getting two equations find intersecting points

another vertex of square is known now ..........

opp vertex of the found one can be found out easily becase of mid point of the diagonal is known which is also midpt of the unfound vertex and found vertex

think so this would help u in solving

my motto is that u should get the concept by hints and try the ans ur self