Concept:The type of conic section depends on the relation between the semi-vertical angle
α and the angle
β between the cutting plane and the cone's axis.
Explanation:For a right circular cone, the conic is determined by comparing
α and
β.
If
0≤β<α, the plane cuts both nappes, giving a hyperbola.
If
β=α, the plane is parallel to a generator, giving a parabola.
If
α<β<90∘, the plane cuts only one nappe, giving an ellipse.
If
β=90∘, the plane is perpendicular to the axis, giving a circle.
Statement-I says
α>β≥0, which is exactly
0≤β<α.
So the section is a hyperbola, and Statement-I is true.
The angle
β is always taken between the plane and the axis, so its valid range is
0∘ to
90∘.
Therefore,
β>90∘ is invalid in this context, so Statement-II is false.
Answer:Statement I is true, Statement II is false.
Hence, the correct option is A.