Here are two $x$,$y$ coordinates: $(2,2)$ ,$(4,3)$. And I want to know if I choose $x$ between above coordinate. How can I know the $y$?

As I know a slope of line equation is like this. $$y= mx+b$$

So if I apply the coordinate into above equation. $$m= \dfrac{3-2}{4-2} = \dfrac{1}{2}$$ $$b= 2$$ $$y= \dfrac{1}{2} x + b$$

So if I choose $x$ to be $4$ then I can get a value $4$ not $3$. I don't know how to resolve this problem.


closed as off-topic by Dima, JRE, lennon310, Phonon Jul 16 '15 at 2:53

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about signal processing within the scope defined in the help center." – Dima, Phonon
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Your $b=1$. Check it.. $\endgroup$ – Oliver Jun 11 '15 at 4:11
  • 1
    $\begingroup$ You kidding, right? This is not a DSP question. $\endgroup$ – jojek Jun 11 '15 at 8:11
  • $\begingroup$ Hmm I don't think so. Becuase my question is from DSP expriment. $\endgroup$ – gmotree Jun 11 '15 at 13:10
  • $\begingroup$ And that obviously doesn't make it fit to the DSP SE. $\endgroup$ – jojek Jun 11 '15 at 15:28
  • 1
    $\begingroup$ I'm voting to close this question as off-topic because it is a general question about simple mathematics. $\endgroup$ – JRE Jul 15 '15 at 9:27

Your $b$ is wrong. Take a look here. The form $y=mx+b$ is called Slope-Intercept form where $b$ is the intersection with the y-axis (which is 1 in your case). You should use the two-point form: $$ y - y_1 = \frac{y_2 - y_1}{x_2 - x_1} (x - x_1) $$

which yields $$ y - 2 = \frac{1}{2} (x - 2) $$ or $$ y = \frac{1}{2} x + 1 $$


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