A nonlinear system has at least one equation that isn't a line, most often a parabola and a line. A solution is an ordered pair (x,y) that makes both equations true, which is a point where the two graphs meet.
Substitute. When both equations start with y=, set the right sides equal. For y=x2−3 and y=2x: x2−3=2x, so x2−2x−3=0, (x−3)(x+1)=0, and x=3 or x=−1.
**Find y too.** Put each x into the simpler equation: y=2(3)=6 and y=2(−1)=−2. The solutions are (3,6) and (−1,−2).
Count with the discriminant. After substituting, the quadratic in x has as many real solutions as the graphs have intersection points. Discriminant positive: the line crosses the parabola twice. Zero: the line just touches it once. Negative: they never meet. For *exactly one solution, what is k?*, set this discriminant to 0.
Reading a graph. When the graphs are given, each intersection point is a solution. A point that is on only one of the graphs, such as the parabola's vertex or the line's y-intercept, is not a solution of the system.