Slope-intercept equation

Question

Find the slope intercept equation of the line with slope -3, passing though point (1,-5). Enter the y-intercept only, as a numeric value.

Answer 1

A line has the following equation:

 

y = a*x + b 

 

where a: slope

          b: y-intercept

 

Your line has a slope of -3 so it can be written as: y = -3*x + b

 

and it passes through point (1,-5):

-5 = -3*1 + b

so b = -5 + 3

b = -2

Answer 2

-3 = slope = rise/run = (y - (-5))/(x - 1)

-3 = (y+5)/(x-1)

 

-3(x-1) = y+5

 

-3x + 3 = y + 5

 

-3x - 2 = y

 

y = -3x - 2

 

y = mx + b, where m = -3 and b = -2.

 

So the y-intercept is -3.