How do you write an equation of a line going through (-1,2), (3,-4)?

1 Answer
Jun 6, 2017

See a solution process below:

Explanation:

First, we need to determine the slope of the line. The slope can be found by using the formula: m = (color(red)(y_2) - color(blue)(y_1))/(color(red)(x_2) - color(blue)(x_1))

Where m is the slope and (color(blue)(x_1, y_1)) and (color(red)(x_2, y_2)) are the two points on the line.

Substituting the values from the points in the problem gives:

m = (color(red)(-4) - color(blue)(2))/(color(red)(3) - color(blue)(-1)) = (color(red)(-4) - color(blue)(2))/(color(red)(3) + color(blue)(1)) = -6/4 = -3/2

Next we can use the point-slope formula to write an equation for the line. The point-slope formula states: (y - color(red)(y_1)) = color(blue)(m)(x - color(red)(x_1))

Where color(blue)(m) is the slope and (color(red)(x_1, y_1)) is a point the line passes through. Substituting the slope we calculated and the values from the second point in the problem gives:

(y - color(red)(-4)) = color(blue)(-3/2)(x - color(red)(3))

(y + color(red)(4)) = color(blue)(-3/2)(x - color(red)(3))

We can also substitute the slope we calculated and the values from the first point in the problem giving:

(y - color(red)(2)) = color(blue)(-3/2)(x - color(red)(-1))

(y - color(red)(2)) = color(blue)(-3/2)(x + color(red)(1))

We can solve this equation for y to write an equation in slope intercept form. The slope-intercept form of a linear equation is: y = color(red)(m)x + color(blue)(b)

Where color(red)(m) is the slope and color(blue)(b) is the y-intercept value.

y - color(red)(2) = (color(blue)(-3/2) xx x) + (color(blue)(-3/2) xx color(red)(1))

y - color(red)(2) = -3/2x + (-3/2)

y - color(red)(2) = -3/2x - 3/2

y - color(red)(2) + 2 = -3/2x - 3/2 + 2

y - 0 = -3/2x - 3/2 + (2/2 xx 2)

y = -3/2x - 3/2 + 4/2

y = color(red)(-3/2)x + color(blue)(1/2)