How do you write an equation of a line given (-3, 1) and (-2, -5)?

1 Answer
Apr 13, 2017

See the entire solution process below:

Explanation:

First, we must 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)(-5) - color(blue)(1))/(color(red)(-2) - color(blue)(-3)) = (color(red)(-5) - color(blue)(1))/(color(red)(-2) + color(blue)(3)) = -6/1 = -6#

We can now use the point slope formula to find 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 first point from the problem gives:

#(y - color(red)(1)) = color(blue)(-6)(x - color(red)(-3))#

Solution 1) #(y - color(red)(1)) = color(blue)(-6)(x + color(red)(3))#

We can also substitute the slope we calculated and the second point from the problem giving:

#(y - color(red)(-5)) = color(blue)(-6)(x - color(red)(-2))#

Solution 2) #(y + color(red)(5)) = color(blue)(-6)(x + color(red)(2))#

We can also solve this for #y# to put the 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)(5) = (color(blue)(-6) xx x) + (color(blue)(-6) xx color(red)(2))#

#y + color(red)(5) = -6x - 12#

#y + color(red)(5) - 5 = -6x - 12 - 5#

#y + 0 = -6x - 17#

Solution 3) #y = color(red)(-6)x - color(blue)(17)#