Question

Find the Error When graphing the equation y=−3x+2, a student plotted the y-intercept at 2, then moved down 3 units and to the left 2 units because the slope is negative, so both rise and run are negative. Find his error and correct it.

Which selections describe an error that the student made and give the correct response? Select all that apply.


Multiple select question.




A)

The student used the y-intercept, 2, for the denominator of the slope. The slope should be −3 or −31 .





B)

The student said that, because the slope is negative, both rise and run are negative. When the slope is negative, either the numerator is negative or the denominator is negative, not both.





C)

The student plotted the y-intercept at 2, instead of at −3. The y-intercept should be −3, because when x=0, you get y=−3.





D)

After plotting the y-intercept at 2, the student moved down 3 units and to the left 2 units. The student should have moved down 3 units and the to the left 1 unit, because the slope is −3−1, not −3−2.





E)

After plotting the y-intercept at 2, the student moved down 3 units and to the left 2 units. The student should have moved down 3 units and the to the right 2 units, because the slope is −32, not −3−2.





F)

After plotting the y-intercept at 2, the student moved down 3 units and to the left 2 units. The student should have moved down 3 units and the to the right 1 unit, because the slope is −31, not −3−2.




*also need this one*

Answer 1

A, B, F

Explanation:

You want to know the errors made in graphing y = -3x +2 by plotting the y-intercept of 2 and then plotting another point 3 down and 2 left of that.

Plot

The appropriate graph would be created by plotting the y-intercept at 2, then moving down 3 units and 1 unit right from there, because the slope is -3.

Errors

The y-intercept is correctly plotted at y=2.

The next point is incorrectly plotted down 3 units and 2 units left of the y-intercept. It should be plotted down 3 units and 1 unit right.

The slope is -3, or -3/1. For a negative slope, the rise or run, but not both, will be negative. We don't know the student's rationale for using 2 as the "run" in ...

slope = rise/run

The best error descriptors seem to be ...

A) The student used the y-intercept, 2, for the denominator of the slope. The slope should be −3 or −3/1 .

B) The student said that, because the slope is negative, both rise and run are negative. When the slope is negative, either the numerator is negative or the denominator is negative, not both.

F) After plotting the y-intercept at 2, the student moved down 3 units and to the left 2 units. The student should have moved down 3 units and the to the right 1 unit, because the slope is −3/1, not −3/−2.

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