Question

Suppose a line has slope -2/3 and passes through the point (1, 8). which other point must also be on the graph?

Answer 1

Answer:   Choice A.   (7,4)

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Explanation:

Use the slope and given point to find the y intercept

y = mx+b

8 = (-2/3)*(1) + b

8 = -2/3 + b

8 + 2/3 = b

24/3 + 2/3 = b

26/3 = b

b = 26/3

The equation of the line is y = (-2/3)x + 26/3

To confirm this, plug in x = 1 and we should get y = 8, due to the point (1,8)

y = (-2/3)x + 26/3

y = (-2/3)*1 + 26/3

y = -2/3 + 26/3

y = (-2+26)/3

y = 24/3

y = 8

So that verifies we have the correct equation.

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Next, go through each answer choice to see if the x coordinate of the point leads to the y coordinate.

If we try x = 7, then,

y = (-2/3)x + 26/3

y = (-2/3)(7) + 26/3

y = -14/3 + 26/3

y = (-14+26)/3

y = 12/3

y = 4

This shows that (7,4) is on the line. Choice A is the answer

That rules out choice B.

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If we tried x = -5, then,

y = (-2/3)x + 26/3

y = (-2/3)(-5) + 26/3

y = 10/3 + 26/3

y = 36/3

y = 12

meaning that (-5,12) is on the line. That rules out choices C and D.

Refer to the graph below. It visually confirms that of the four answer choices, only point A is on the line. I used GeoGebra to make the graph.