slope of a line

Question

David was given the slope of a line m = -4 and a point (-2, 3). He determined that the equation of the line in point slope form was y + 2 = -4(x − 3). Distinguish whether David is correct or not with the equation he created.

Answer 1

The point-slope form is:

y-y₁ = m(x-x₁)

 

Substitute -4 for m, -2 for x₁ and 3 for y₁.  (-2,3) is an (x,y) coordinate pair.

y-3 = -4[x-(-2)]

y-3 = -4(x+2)

 

David got it wrong.  He swapped the x and y.

NOTE: This is a really common error!  Since the y appears first in the point-slope equation, it's really easy to put the first number in the given point's coordinates (the x value) in the y position.