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# Slope-intercept equation from slope & point (old)

An old video where Sal finds the slope-intercept form of a line that has a slope of 7 and goes through the point (-4,-11). Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• Doesn't the steepness of a slope depend on the marginal value of units on a given graph? So the steepness of a slope of (7) could be very steep (if numbered by units of one) or not steep at all (if numbered by units of 100). (I believe advertisers use this trick to fool people on rises and falls of certain markets)
• Mo,
The steepness would be the same no matter which units you use.
If you used units of 100, you would go over 100 and up 700.
In you used units of 1/10, you would go over 1/10 and up 7/10.

In fact, if the line goes through the origin, the points (1/10 , 7/10) and (100,700) would both be on the line. The steepness of the line would be a slope of 7.
The steepness of the line would be the exact same.

But, yes, advertisers and others do often use math misconceptions to mislead people.
• What is the m and what is the b in y=mx+b?
• m is the slope and b is the y-intercept.
• How does a linear equation become undefined. Can it go on forever, and can it be negative? Also, why is the y-axis undefined, but the x-axis is different. What is the reason behind that?
• Hi Amogh Mandava!

When finding the slope of a line using the slope formula (y2-y1/x2-x1), the slope of a vertical line would be (y/0). However, division by zero is undefined. Hence, the equation's slope is undefined. However, for a horizontal line, the slope formula would end up (0/x). A number divided by zero is zero. Thus, we can determine that a horizontal line's slope is 0.
slr
(1 vote)
• So the answer to this question would be in equation form? And all we have to figure out is m and b, right?
• Hey! I haven't practiced math in over ten years and am now preparing for the GMAT. Your videos have been invaluable in the refreshing process: my memory thanks you. Actually, I have a number of friends that are currently preparing for the GMAT and they all use your videos. Keep it up!
• why couldn't a vertical line have a equation something like y=(ifinity/0)x+0 which I know a number divided by 0 is undefined I was just wandering if this would define a vertical line with an equation
(1 vote)
• The problem isn't coming up with an equation. For example, the equation of a vertical line through the point (3,0) is x=3. The problem is that the slope of the line is undefined, because we get zero in the denominator of a fraction. It's natural to feel there's something unsatisfactory in this state of affairs and wonder if there might be some way around it, but in the end it's just a fact of life we have to accept.
• Is the equation y=mx+b interchangeable with x=my+b with "b" as the x intercept?
(1 vote)
• No, the value of m and b will be different for most equations.
• How Would We Solve y=mx-2
(1 vote)
• This is the equation of a line on a graph, to solve this you must realise, the equation can also be written as 1y=1m1x-2. Y= The location of the point on the Y axis. X= The location of the point on the X axis. M= The slope. -2= Is the Y intercept, If there is a graph you can replace X and Y with the real co-ordinates, Ex: X=3 Y=5 5=3x-2. I hope it helps, that's how I'd solve it. :D