Grace R.
asked 01/21/14Equation 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.
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2 Answers By Expert Tutors

Vivian L. answered 01/21/14
Tutor
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Microsoft Word/Excel/Outlook, essay composition, math; I LOVE TO TEACH
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

Hafid M. answered 01/21/14
Tutor
4.3
(9)
Experienced Science and Math Tutor
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
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Grace R.
01/21/14