Given that these simultaneous equations x - y = k
x² + y² – 9=0
have exactly one pair of solutions, show that k = +3V2.

Thank you for the help :)

Which statement is true? a.the graph of a two-variable equation is the set of all points in the coordinate plane that solve the equation.b.the graph of a two-variable equation consists of only two points: one with a zero y-coordinate, (a,0), and one with a zero x-coordinate, (0,b).c.the graph of a two-variable equation is the set of all positive points that solve the equation.d.the graph of a two-variable equation is a single point that solves the equation.