Question 9 - MCQs from NCERT Exemplar - Chapter 3 Class 10 Pair of Linear Equations in Two Variables

Transcript

Question 9 If the lines given by 3x + 2ky = 2 and 2x + 5y + 1 = 0 are parallel, then the value of k is (A) (−5)/4 (B) 2/5 (C) 15/4 (D) 3/2 3x + 2ky − 2 = 0 Comparing with a1x + b1y + c1 = 0 ∴ a1 = 3 , b1 = 2k , c1 = −2 2x + 5y + 1 = 0 Comparing with a2x + b2y + c2 = 0 ∴ a2 = 2 , b2 = 5, c2 = 1 Therefore, a1 = 3 , b1 = 2k , c1 = −2 & a2 = 2 , b2 = 5, c2 = 1 𝑎1/𝑎2 = 3/2 𝑏1/𝑏2 = 2𝑘/5 𝑐1/𝑐2 = (−2)/1 𝑐1/𝑐2 = −2 Since the lines are coincident 𝒂𝟏/𝒂𝟐 = 𝒃𝟏/𝒃𝟐 ≠ 𝒄𝟏/𝒄𝟐 3/2=2𝑘/5≠1/2 Thus, 3/2=2𝑘/5 3/2 × 5/2 = k k = 𝟏𝟓/𝟒 So, the correct answer is (C)