Question the-gr

1.3 Linear Equations in Two Variables - Writing equations from data/points
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The graph of y=fx-11 is shown.

  • The line slants sharply down from left to right.
  • The line passes through the following points:
    • (negative 1 comma negative 2)
    • (0 comma negative 4)

Which equation defines the linear function f ?

A.

fx= - 13 x - 11

B.

fx= - 2 x + 7

C.

fx= - 13 x + 7

D.

fx= - 2 x - 11

The graph of y = f x - 11 is shown. The line slants sharply down

Hard-difficulty · SAT Math · Linear Equations in Two Variables — Writing equations from data/points. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice B is correct. The graph of a line in the xy-plane can be represented by the equation y=mx+b, where m is the slope of the line and 0,b is the y-intercept. The slope of a line that passes through the points x1,y1 and x2,y2 can be calculated using the formula m=y2-y1x2-x1. The line shown passes through the points -1,-2 and 0,-4. Substituting -1,-2 and 0,4 for x1,y1 and x2,y2, respectively, in the formula m=y2-y1x2-x1 yields m=-4--20--1, which is equivalent to m=-21, or m=-2. Since the line shown passes through the point 0,-4, it follows that b=-4. Substituting - 2 for m and - 4 for b in the equation y=mx+b yields y=-2x-4. It’s given that the graph shown is the graph of y=fx-11. Substituting -2x-4 for y in the equation y=fx-11 yields -2x-4=fx-11. Adding 11 to both sides of this equation yields -2x+7=fx. Therefore, the equation fx=-2x+7 defines the linear function f .

Choice A 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.