Why is it called two real and equal roots b^2 - 4ac = 0 when the straight line touches the curve at one point?

b^2 - 4ac = 0, also defined as two real and equal roots (TWO ROOTS) but why for its graph, the U parabola or curve touches the line at only one point (ONE)
Two roots on one point? Senseless. But it will make sense when b^2 - 4ac > 0; two real and distinct roots; intersects at two points.

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