Question for-th

1.4 Systems of Two Linear Equations - Graphical solution of two lines
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  • 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 x + 4 y = -16 , how many solutions x,y will the resulting system of three equations have?

A.

Zero

B.

Exactly one

C.

Exactly two

D.

Infinitely many

For the first line in the system: The line slants gradually down from left to right.

Hard-difficulty · SAT Math · Systems of Two Linear Equations — Graphical solution of two lines. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

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 x,y is a solution to the system, the point x,y 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 8,2.  It follows that if a new graph of three linear equations is created using the system of equations shown and the graph of x+4y=-16, this system has either zero solutions or one solution, the point 8,2. Substituting 8 for x and 2 for y in the equation x+4y=-16 yields 8+42=-16, or 16=-16. Since this equation is not true, the point 8,2 does not lie on the graph of x+4y=-16. Therefore, 8,2 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.