(a) If a point belong to the curve , then . Then for the point we have , and thus the point is also belong to the curve . Consequently, the curve is symmetric with respect to the origin.
Answer: true
(b) Since the vector is parallel to the line and , we conclude that
Answer: true
(c) The general equation of a hyperbola is
.
Let us find the section of by the plane :
Since the eqution has no real solution, the plane does not intersect . The equation is not a hyperbola equation.
Answer: false
(d) The xy-plane intersects the sphere in a great circle if and only if the center of this sphere belong to -plane. Let us rewrite the equation of the sphere in the the following form: It follows that is the center of the sphere. Taking into account that the third coordinate of is not equal to 0, we conclude that the center of the sphere does not belong to the -plane, and therefore, the sphere does not intersect the -plane in a great circle.
Answer: false
(e) Let consider any line segment with The projection of a line segment on another line is the line segment formed by the projections of the end points of the line segment on this line. If we choose such a line that the segment is perpendicular to , then the points A and B projects on the same point of the line , and therefore, .
Answer: false
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