Find the y-intercept?

Question

I need to know how to find the y-intercept when given two points. (4,3) (-4,-4)

I got that it was -1/2 but my sister got -1. Which one is correct, or are we both wrong?

Answer 1

I would create the equation of the line:

y-yo = m(x-x0)

m is the slope which is (y1-y0)/(x1-xo):

(-4-3)/(-4-4) = -7/-8 = 7/8, and putting this into the line is

y-3=(7/8)(x-4)
y-3 = (7/8)x - 28/8 - now 28/8 = 7/2
y = (7/8)x - 7/2 + 3
y = (7/8)x - 1/2

(double check that the given points actually work in the equation to make sure you've got it correct).

Now finally, the y-intercept occurs when x = 0, so just plug this value into your equation:

y = (7/8)*0 - 1/2
y = 1/2 - so your answer is correct.

BTW - it doesn't matter which points you choose as xo, yo or x1,y1 as you will end up with the same answer for the slope - just make sure you're consistent. I tend to avoid subtracting negative answers as it makes for less potential errors, hence I chose the order I did above.

Answer 2

The slope of the line that passes through (4,3) and (-4,-4) is (-4-3) /(-4-4), =-7/ -8, =7/8
The equation is y=(7/8)x+b.
Since (4,3) lies on the line, (you can use (-4,-4) if you wish), it satisfies the equation for the line.
Therefore, 3=(7/8)(4) +b
3-28/8=b
24/8-28/8=b
-4/8=b
-1/2=b
b of course IS the y intercept,so the answer you got of -1/2 is right.

Answer 3

this is a rather simple problem. all u have to do is graph the two points and make a line. ur vertical axis is the y axis and the horizontal one is the x axis. when u graph it u put the two points on the graph then u draw a line. and wherever the line crosses the y axis, that is ur y intercept. and u were right by the way

Answer 4

m = (- 4 - 3) / (- 4 - 4)
m = - 7 / - 8
m = 7 / 8
y - 3 = (7/8) (x - 4)
y = (7/8) x - 7/2 + 3
y = (7/8)x - 1/2
y is intercept is y = - 1 / 2
(bad luck sis!)

Answer 5

y2-y1
-------=y int
x2-x1