Compare the size with the square of radius and the square of the distance from point to straight line, and indirectly compare the size of radius with the distance from point to straight line.
Radius-distance =0 tangent, because radius = distance.
Radius-distance > 0, radius > distance is intersection,
There is another situation that will not be listed.
As for your discriminant of less than 0.
When a≠0, 7a? -4a+7=0 is a quadratic function of opening upward.
And because the equation has no root, that is, it has no intersection with the X axis, that is, 7a? -4a+7>0
When a=0, 7 is always greater than 0.
Finally, 9-d? > 0, which means 9 > d? Finally, the radius > the distance from the center of the circle to the straight line is obtained.
Finally got the answer, intersect
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