To put it bluntly, quadratic equation is a special case of quadratic function that makes y=0. So △ = b 2-4ac can be said to be a quadratic function or a discriminant of a quadratic equation. Judging whether the equation has a root is actually a question of judging whether the image of the quadratic function intersects with the straight line y=0. When b? -4ac & lt； 0, no solution, that is, no intersection. When b? When -4ac=0, there is a solution, which just intersects. When b? -4ac & gt； 0, there are two solutions; There are two different intersections.