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Linear and Quadratic Equations · Question 19 of 66

Question 19

MediumOriginal question

For what value of kk does the pair 2x+ky=72x + ky = 7 and 6x+15y=116x + 15y = 11 have no solution?

Options for question 19

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. No solution means parallel lines: a1a2=b1b2≠c1c2\frac{a_1}{a_2} = \frac{b_1}{b_2} \neq \frac{c_1}{c_2}.

  2. 26=k15\frac{2}{6} = \frac{k}{15}, so k=153=5k = \frac{15}{3} = 5.

  3. Check the constants: 711≠13\frac{7}{11} \neq \frac{1}{3}, so the lines are parallel and distinct.

Worth noting

45 comes from turning the ratio upside down (k15=3)(\frac{k}{15} = 3). 10511\frac{105}{11} comes from matching kk with the constants' ratio instead of the xx ratio. 15 assumes the coefficients themselves must be equal; only their ratios must match.

Concept
Condition for a pair of linear equations to have no solution
Typical time
70 s
Your time
—
The rule this testsPairs of linear equations
Practise this chapter →

Ten questions from Linear and Quadratic Equations, at your own pace.

Practise this chapter →

Ten questions from Linear and Quadratic Equations, at your own pace.