On x-axis, y = 0, so if it intersects x-axis, then ax² + bx + c = 0sud21 wrote:In xy-plane, Y=ax^2+bx+c,does the graph intersect with X axis?
1). a>0
2). c<0
If b² - 4ac > 0, then we have two distinct real roots.
(1) a > 0 does not imply if the graph intersects with x-axis; NOT sufficient.
(2) c < 0 does not imply if the graph intersects with x-axis; NOT sufficient.
Combining (1) and (2), we know that b² will always be positive and (-4ac) will also be positive, so b² - 4ac > 0; SUFFICIENT.
The correct answer is C.
