Why must K be greater than 0 and why can't K be less than 0 in senior one cohesion mathematics? Why should we assume that A is greater than 0 in the unary quadratic inequality?
When k < 0, the binary inequality is a parabola with a downward opening, and there are two cases. One is that the vertex is below the X axis, and the number on the line is less than 0. The other is that the vertex is above or on the X axis, so it will eventually intersect with the X axis until it is less than 0. The inequality in the topic is always positive, so k must be greater than 0.