Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Write an equation of the line in slope-intercept form, the line passing through $(-1, 3)$ and $(-4, 5)$. I know that $y=mx + b$ and the slope is $2/3$ but when I plug in the points $3=\frac23 (-1)+b$ to find $b$, I keep getting answers that don't make sense. Graphing hasn't helped either. Just wondering what I am doing wrong.

share|cite|improve this question
You calculated the slope incorrectly. – dfeuer Jul 16 '13 at 23:57

The slope $m$ is calculated as follows:

$m = (y_2 - y_1) / (x_2 - x_1) = (5 - 3) / (-4 - (-1)) = -2/3$, not $2/3$.

Then you can substitute one of the point's values and $m$ to find $b$.

$y = mx + b$

$5 = -2/3(-4) + b$

$5 = 8/3 + b$

$b = 7/3$

share|cite|improve this answer
That is what i kept getting but the teacher said b=5 – Savannah Jul 17 '13 at 0:39
@Savannah Then it seems your teacher is wrong. – Alraxite Jul 17 '13 at 1:00

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.