Search 75,896 tutors
FIND TUTORS
Ask a question
0 0

Equation of the line. Slope-intercept

find the equation of the line containing the given points (1,3) and (-3,-7). Express your answer in slope-intercept form.

Comments

How do you know which one is Y2? or Y1?
 
Should it look something like this:
 
-7-3
_____
-3-1
Thank you both for your responses; however, this is a lot to remember. Is there an easier way? I am really horrible with math, always have been since 3rd grade when calculators were introduced (I stopped using my brain at that point), please help me find an easier solution.
There is no rule as to which one is y1 or y2.  Your equation for slope is correct.  It will produce the result of -10/-4 which is 10/4 which is 2.5.  This is the same result we reached.
 
I know it seems difficult.  But you will conquer it with enough practice.
Thanks again for replying. I really appreciate the help :) I will check out the videos. 

Comment

Tutors, please sign in to answer this question.

2 Answers

Hi Grace;
(1,3) and (-3,-7)
The slope is defined as the change-of-y divided by the change-of-x...
(y-y1)/(x-x1)
(3--7)/(1--3)
Subtracting a negative number is the same as adding a positive number...
(3+7)/(1+3)
10/4
2.5
Let's take one point and apply the point-slope formula.  This will expand into the slope-intercept formula.  I randomly select the first point...
(y-y1)=m(x-x1)
(y-3)=2.5(x-1)
y-3=2.5x-2.5
Let's add 3 to both sides...
3+y-3=2.5x-2.5+3
y=2.5x+0.5
This is slope-intercept format of...
y=mx+b, m is the slope and b is the y-intercept, the value of y when x=0.
Let's plug-in the other point to verify formula...
-7=[2.5(-3)]+0.5
-7=-7.5+0.5
-7=-7
 
 
 
Slope intercept form is the form y= mx+b
where m is the slope and b is the y-intercept.
 
First, find your slope and plug into the form above
 
slope can be remembered as "rise over run."  and your "rise" will be Y2-Y2 or  3-(-7) = 10
the "run" will be X2- X1 or 1 - (-3) = 4
 
therefore the slope is (Y2 - Y1 ) / (X2 - X1)  = 10/4 or 2.5
 
Now plug into the slope intercept form using either of your original points.  I picked the point (1,3)
 
y = mx + b
3 = (2.5)(1) + b   now you must solve for b
3 = 2.5 + b and b = 0.5
 
Therefore the equation of the line is y = 2.5x + 0.5