Question

Write the equation of a line in the slope-intercept form that contains the points A (1, 2) and B (2, 4).

Answer 1

Answer: Choice A)  y = 2x

slope = 2, y intercept = 0

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Explanation:

We can see this by noting that each y coordinate is simply doubled that of the x coordinate.

• x = 1 doubles to y = 2
• x = 2 doubles to y = 4

So in general, x doubles to 2x to get the y coordinate. Therefore, y = 2x.

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Alternative method:

A more thorough step by step process would have us first finding the slope

m = (y2 - y1)/(x2 - x1)

m = (4 - 2)/(2 - 1)

m = 2/1

m = 2 is the slope

Use this slope value along with one of the points to find b. I'll use the point (x,y) = (1,2)

So,

y = mx+b

2 = 2*1+b

2 = 2+b

2-2 = b

0 = b

b = 0 is the y intercept

We go from y = mx+b to y = 2x+0, which simplifies to y = 2x