Question

To solve the system of linear equations 3 x minus 2 y = 4 and 9 x minus 6 y = 12 by using the linear combination method, Henry decided that he should first multiply the first equation by –3 and then add the two equations together to eliminate the x-terms. When he did so, he also eliminated the y-terms and got the equation 0 = 0, so he thought that the system of equations must have an infinite number of solutions. To check his answer, he graphed the equations 3 x minus 2 y = 4 and 9 x minus 6 y = 12 with his graphing calculator, but he could only see one line. Why is this?

A. because the system of equations actually has only one solution
B. because the system of equations actually has no solution
C.because the graphs of the two equations overlap each other
D. because the graph of one of the equations does not exist

Answer 1

9514 1404 393

Answer:

C. because the graphs of the two equations overlap each other

Explanation:

When a system of linear equations has an infinite number of solutions, the equations are "dependent." That means they both describe the same line. The graph will appear to be one line because the lines overlap each other.

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Additional comment

The Desmos graphing calculator lets the texture of the graph be varied, so we can see that the two lines overlap. In the attached, one equation is graphed as a dotted red line, the other as a solid blue line.