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Which of the following pair of linear equations is / are inconsistent?

(A) x−y=5x - y = 5; 3x−3y=103x - 3y = 10

(B) 2x+3y=42x + 3y = 4; 4x+6y=84x + 6y = 8

(C) 9x+6y=69x + 6y = 6; 3x+2y=33x + 2y = 3

(D) 2x+5y=22x + 5y = 2; 6x−15y=46x - 15y = 4

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 4

A pair a1x+b1y=c1a_1x+b_1y=c_1, a2x+b2y=c2a_2x+b_2y=c_2 is inconsistent when a1a2=b1b2≠c1c2\frac{a_1}{a_2}=\frac{b_1}{b_2}\ne\frac{c_1}{c_2}.

(A): ratios 13=−1−3≠510\frac{1}{3}=\frac{-1}{-3}\ne\frac{5}{10} → inconsistent. (B): all ratios equal 12\frac{1}{2} → coincident (many solutions). (C): 93=62=3≠63=2\frac{9}{3}=\frac{6}{2}=3\ne\frac{6}{3}=2 → inconsistent. (D): 26=13≠5−15=−13\frac{2}{6}=\frac{1}{3}\ne\frac{5}{-15}=-\frac{1}{3} → consistent (unique solution).

So only (A) and (C) are inconsistent.

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