MCQMediumJEE 2024Straight Line Equations

JEE Mathematics 2024 Question with Solution

The values of α\alpha for which lines 2xy+3=02x - y + 3 = 0, 6x+3y+1=06x + 3y + 1 = 0, and ax+2y2=0ax + 2y - 2 = 0 do not form a triangle are:

  • A

    (2,1)(-2,1)

  • B

    (3,0)(-3,0)

  • C

    (32,32)\left(-\frac{3}{2}, \frac{3}{2}\right)

  • D

    (0,3)(0,3)

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: The lines are 2xy+3=02x - y + 3 = 0, 6x+3y+1=06x + 3y + 1 = 0, and ax+2y2=0ax + 2y - 2 = 0.

Find: The values of α\alpha for which these three lines do not form a triangle.

For three lines to not form a triangle, either two of them must be parallel or all three must be concurrent.

From the solution, checking parallelism:

2a=12\frac{2}{a} = \frac{-1}{2}

gives

a=4a = -4

and

6a=32\frac{6}{a} = \frac{3}{2}

gives

a=4a = 4

So the values obtained from the working are 4-4 and 44.

The solution is inconsistent with the listed options, and the answer key points to option B. Since the extracted solution does not support any listed option value, the correct option cannot be resolved reliably from the supplied content.

Consistency Check

The solution appears to belong to a different version of the question. It discusses the sum of squares of values of α\alpha and concludes with 3232, whereas the present question asks for the values of α\alpha themselves and provides ordered-pair options.

Also, the solution uses both aa and α\alpha inconsistently. Because of this mismatch, the final option cannot be mapped with confidence. Hence the answer is marked AMBIGUOUS.

Common mistakes

  • Assuming that lines fail to form a triangle only when two lines are parallel. They may also fail to form a triangle when all three lines are concurrent. Always check both conditions.

  • Using the parallel condition incorrectly. For lines a1x+b1y+c1=0a_1x + b_1y + c_1 = 0 and a2x+b2y+c2=0a_2x + b_2y + c_2 = 0, parallelism requires a1a2=b1b2\frac{a_1}{a_2} = \frac{b_1}{b_2}, not involving constants first.

  • Trusting a mismatched solution blindly. Here the solution concludes a numerical value 3232, which does not match the asked format of values of α\alpha. Always verify that the solution corresponds to the same question.

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