SOLUTION: Hi! So my problem is: Write an equation for the line with slope 3 going through the point (1,-2). THe answer that I got for it was y=3x-b, but it was wrong. Please help me, Than

Algebra ->  Coordinate-system -> SOLUTION: Hi! So my problem is: Write an equation for the line with slope 3 going through the point (1,-2). THe answer that I got for it was y=3x-b, but it was wrong. Please help me, Than      Log On


   



Question 130380This question is from textbook algebra
: Hi!
So my problem is: Write an equation for the line with slope 3 going through the point (1,-2).
THe answer that I got for it was y=3x-b, but it was wrong.
Please help me, Thank you=)
This question is from textbook algebra

Found 2 solutions by jim_thompson5910, solver91311:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

If you want to find the equation of line with a given a slope of 3 which goes through the point (1,-2), you can simply use the point-slope formula to find the equation:


---Point-Slope Formula---
y-y%5B1%5D=m%28x-x%5B1%5D%29 where m is the slope, and is the given point

So lets use the Point-Slope Formula to find the equation of the line

y--2=%283%29%28x-1%29 Plug in m=3, x%5B1%5D=1, and y%5B1%5D=-2 (these values are given)


y%2B2=%283%29%28x-1%29 Rewrite y--2 as y%2B2


y%2B2=3x%2B%283%29%28-1%29 Distribute 3

y%2B2=3x-3 Multiply 3 and -1 to get -3

y=3x-3-2 Subtract 2 from both sides to isolate y

y=3x-5 Combine like terms -3 and -2 to get -5
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Answer:


So the equation of the line with a slope of 3 which goes through the point (1,-2) is:

y=3x-5 which is now in y=mx%2Bb form where the slope is m=3 and the y-intercept is b=-5

Notice if we graph the equation y=3x-5 and plot the point (1,-2), we get (note: if you need help with graphing, check out this solver)

Graph of y=3x-5 through the point (1,-2)
and we can see that the point lies on the line. Since we know the equation has a slope of 3 and goes through the point (1,-2), this verifies our answer.

Answer by
solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
The reason your answer is wrong is that your equation represents an infinite number of lines, one for every possible value of b which is the set of real numbers. You have to find the particular y-intercept that is a point on the same line that passes through the point (1,-2).

When you are given the slope and a single point, use the point-slope form of the line:

y-y%5B1%5D=m%28x-x%5B1%5D%29 where red%28x%5B1%5D%29 and red%28y%5B1%5D%29 are the coordinates of the given point and green%28m%29 is the given slope.

y-red%28%28-2%29%29=green%283%29%28x-red%281%29%29

Now you can either leave it like that, put it into slope-intercept form by solving for y, or put it into standard form (Ax%2BBy=C).

Slope-intercept form:
y%2B2=3%28x-1%29
y%2B2=3x-3
y=3x-5 (Do you see the difference between this answer and your answer?)

Standard Form:
y%2B2=3%28x-1%29
y%2B2=3x-3
-3x%2By=-5
3x-y=5