Maths · Coordinate geometry · chapter 9 of 14

Class 11 Maths Chapter 9: Straight Lines Assertion-reason questions with answers

2 assertion-reason questions on Straight Lines, 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 lines y = 3x − 5 and 6x − 2y + 1 = 0 are parallel. Reason (R): Two non-vertical lines are parallel if and only if their slopes are equal.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

6x − 2y + 1 = 0 is y = 3x + 1/2, slope 3, the same as y = 3x − 5. Equal slopes are exactly the condition in R, so R explains A.

Question 2
Assertion (A): The points (0, 0), (2, 6) and (−1, −3) are collinear. Reason (R): The slope of the y-axis is not defined.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

A is true: slope from (0, 0) to (2, 6) is 3 and from (0, 0) to (−1, −3) is 3, with a common point. R is true (the y-axis is vertical), but it says nothing about why these three points are collinear.

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