If the lines \(x+y=9\) and \(kx+3y=23\) both pass through the point \(\left(4,5\right)\), what is the value of \(k\)?
Answer and explanation
Correct answer: 2
The coordinates of a point lying on a line must satisfy the equation of that line. Substituting \(\left(4,5\right)\) into the second line, \(kx+3y=23\), gives \(4k+3(5)=23\), or \(4k+15=23\). Thus, \(4k=8\) and \(k=2\). The first equation is also verified because \(4+5=9\). Exam tip: To find an unknown parameter when a point lies on a line, substitute the point’s coordinates directly into the line equation.
Frequently asked questions
What is the correct answer to this question?
2
Why is this the correct answer?
The coordinates of a point lying on a line must satisfy the equation of that line. Substituting \(\left(4,5\right)\) into the second line, \(kx+3y=23\), gives \(4k+3(5)=23\), or \(4k+15=23\). Thus, \(4k=8\) and \(k=2\). The first equation is also verified because \(4+5=9\). Exam tip: To find an unknown parameter when a point lies on a line, substitute the point’s coordinates directly into the line equation.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Pair of Linear Equations in Two Variables. Topic: Algebraic methods: Substitution method and Elimination method..
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