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Systems of two linear equations in two variables SAT question

Math · Algebra · Hard · Answer it here, explanation included.

  • For the first line in the system:
    • The line slants gradually down from left to right.
    • The line passes through the following points:
      • (negative 4 comma 5)
      • (0 comma 4)
      • (8 comma 2)
  • For the second line in the system:
    • The line is horizontal.
    • The line passes through the following points:
      • (0 comma 2)
      • (8 comma 2)

If a new graph of three linear equations is created using the system of equations shown and the equation , how many solutions will the resulting system of three equations have?

ExplanationShow

Choice A is correct. A solution to a system of equations must satisfy each equation in the system. It follows that if an ordered pair  is a solution to the system, the point  lies on the graph in the xy-plane of each equation in the system. The only point that lies on each graph of the system of two linear equations shown is their intersection point .  It follows that if a new graph of three linear equations is created using the system of equations shown and the graph of , this system has either zero solutions or one solution, the point . Substituting for and for in the equation yields , or . Since this equation is not true, the point  does not lie on the graph of . Therefore,  is not a solution to the system of three equations. It follows that there are zero solutions to this system.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.

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