Re: Y-intercept
Petenerd said:
I need help finding the y intercepts of these points.
(-1,3), (1,-1)
(-6,2), (0,4)
(0,3), (5,0)
thanks
You COULD graph each of these lines, and try to determine FROM THE GRAPH where the line crosses the y-axis (the y-intercept). But graphing is tedious and notoriously inaccurate, lots of times.
So...I'll help you with the first one. Let's write the equation of the line through the two points (-1, 3) and (1, -1).
Start by finding the slope. The slope of the line through (x[sub:3eenav3l]1[/sub:3eenav3l], y[sub:3eenav3l]1[/sub:3eenav3l]) and (x[sub:3eenav3l]2[/sub:3eenav3l], y[sub:3eenav3l]2[/sub:3eenav3l]) can be found using this formula, where "m" is the slope:
m = (y[sub:3eenav3l]2[/sub:3eenav3l] - y[sub:3eenav3l]1[/sub:3eenav3l])/(x[sub:3eenav3l]2[/sub:3eenav3l] - x[sub:3eenav3l]1[/sub:3eenav3l])
m = (-1 - 3) / [1 - (-1)]
m = (-4) / (2)
m = -2
Now, use the slope-intercept form of the equation of a line,
y = mx + b
"m" is the slope, and "b" is the y-intercept.
We know the slope is -2. Substitute -2 for "m":
y = -2x + b
We now need to find "b". Since we know that the point (1, -1) is on the line, the equation must be true when x = 1 and y = -1. Substitute 1 for x and -1 for y:
y = -2x + b
-1 = -2(1) + b
-1 = -2 + b
Solve this for "b". Add 2 to both sides of the equation:
-1 + 2 = -2 + b + 2
1 = b
So, the slope-intercept form for the equation of this line is
y = -2x + 1
OH...you wanted the y-intercept for this line, right?? WELL..."b" is the y-intercept...and that is 1!