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Class 11 Maths Chapter 11: Introduction to Three Dimensional Geometry Assertion-reason questions with answers

2 assertion-reason questions on Introduction to Three Dimensional Geometry, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern and JEE Main, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): The point (0, −5, 2) lies in the YZ-plane. Reason (R): The x-coordinate of a point is its perpendicular distance from the YZ-plane.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. The x-coordinate of (0, −5, 2) is 0, so by R its distance from the YZ-plane is zero: the point lies in that plane. R explains A.

Question 2
Assertion (A): The points (1, 2, 2), (2, 1, 2) and (2, 2, 1) are all at a distance of 3 units from the origin. Reason (R): The points (1, 2, 2), (2, 1, 2) and (2, 2, 1) all lie in octant I.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

A is true: for each point x2 + y2 + z2 = 1 + 4 + 4 = 9, so the distance is 3. R is true, since all coordinates are positive. But lying in octant I says nothing about the distance from O; A follows from the distance formula, not from R.

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