Slope question

Question

ok I'm stumped. if we have a(-1,4) and b(3,-2) the y intercept comes out to 5.5 which makes no sense because it clearly doesn't cross through 5.5. please help

Answer 1

If the line passes through (-1,4) and (3,-2), its slope is

 

m = (-2 - 4)/[3 - (-1)] = -6/4 = -3/2

 

y = mx + b

 

y = (-3/2)x + b

 

Find b from either point.  Using (-1,4) you get

 

4 = (-3/2)(-1) + b

 

b = 4 - 3/2 = 8/2 - 3/2 = 5/2

 

y = (-3/2)x + 5/2

 

The y intercept is (0,b), which is (0,5/2)