Lesson: Slope

Comment on Slope

Isn't the slope formula (y2-y1)/(x2-x1)?
greenlight-admin's picture

Both formulas will yield the slope.

Notice that it really comes down to which point you choose to be (x1, y1) and which point you choose to be (x2, y2).

I cover this at 2:52 in the video.

^^^^Mind blown! I never knew that. Thanks!

Please let me know in a negative slope do the y-intercept of the line, y =mx + c is always negative?
greenlight-admin's picture

A negative slope means the line goes down as we move from left to right.
We can move this line up to have a positive y-intercept, and we can move this line down to have a negative y-intercept

See: https://imgur.com/zB3wsb8

Cheers,
Brent

Thanks,

Moreover can I write slope = - (y intercept)/(x intercept) in case of positive slope
and slope = + (y intercept)/(x intercept) in case of negative slope
greenlight-admin's picture

Great idea!
Your formula works for positive slopes, but not negative slopes.

In fact, in BOTH cases, slope = -(y-intercept)/(x-intercept)

Cheers,
Brent

Thanks Brent, but I am really confused in this form plz could you let me know if my reasoning is correct for the question, using this concept
https://gre.myprepclub.com/forum/topic11348.html

Since slope = -(y-intercept)/(x-intercept), the x-intercept has to be negative such that (slope)(y-intercept) > 0

but if y intercept is negative, then x has to be negative as well such that (slope)( y intercept) > 0

Plz if you can solve this with the intercept formula or should I neglect this approach

Thanks
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/topic11348.html

In a different forum, you noticed that slope = -(y-intercept)/(x-intercept)

So, let's use it here (for statement i)

In order for (the slope of line k)(the y-intercept of line k) to be POSITIVE, there are 2 possible cases:
CASE A: the slope and y-intercept are both POSITIVE
CASE B: the slope and y-intercept are both NEGATIVE

CASE A: the slope and y-intercept are both POSITIVE
Our formula, slope = -(y-intercept)/(x-intercept), becomes: POSITIVE = -(POSITIVE)/(x-intercept)
This means the x-intercept must be NEGATIVE

CASE B: the slope and y-intercept are both NEGATIVE
Our formula, slope = -(y-intercept)/(x-intercept), becomes: NEGATIVE= -(NEGATIVE)/(x-intercept)
This means the x-intercept must be NEGATIVE

So, in each of the two possible cases, the x-intercept is NEGATIVE.
So, it MUST BE TRUE that the x-intercept is NEGATIVE

So, statement i is TRUE

Thanks very much Brent

Slope of line k > 0 was also true
Please explain
greenlight-admin's picture

Statement C actually reads "|slope of line k| > 0" [note the absolute value symbols]

KEY: Since the absolute value of a number is almost always positive, the only way that statement C is false is if the slope of line k is zero.

Since we're told that (the slope of line k)(the y-intercept of line k) > 0, we know that the slope of line k is NOT zero.

So, it must be true that |slope of line k| > 0

Does that help?

Cheers,
Brent

Can you explain the relationship between slope and distance between two points?
greenlight-admin's picture

There is no relationship between the slope and the distance between two points.

For example, a line segment with length 5 can have ANY slope imaginable.

Does that help?

Cheers,
Brent

Hello Brent,
Which of the following could be the slope of a line that passes through the point (–2, –3) and crosses the y-axis above the origin?
In that question the slope is 3/2 because the points are -(-2,-3) so it means That the slope is Y/X in this case ?
Thanks !
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/which-of-the-following-could-be-the-slo...
(in the future, please provide the link)

In my solution, we start by examining what the line's slope WOULD be IF it were to pass through the origin (0,0).
IF that were the case, the slope = (-3 - 0)/(-2 - 0) = (-3)/(-2) = 3/2

Since we're told that the line actually crosses the y-axis ABOVE the origin, we know that the line's slope is greater than 3/2

Does that help?

Cheers,
Brent

hi! I'm wondering about this statement: "As the magnitude of slope increases, the line gets steeper". But for a line with a negative slope, this is not the case right? Slope of -5 is a steeper line than a line with slope of -1...could you explain this please?
greenlight-admin's picture

The magnitude of a number is the same as the number's distance from zero on the number line (aka, the number's absolute value)

So, 5 has a greater magnitude than 2.
Likewise, -5 has a greater magnitude than -2.
Likewise, -7 has a greater magnitude than 3.

Since -5 has a greater magnitude than -1, we can conclude that a line with slope -5 is steeper than a line with slope -1.

Does that help?

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