In the standard (x,y) coordinate plane, a line passes through the points (1,-2) and (5,10). At which of the following points does the line cross the y-axis?
a. (-8,0)
b. (-5,0)
c. (0,0)
d. (0,-8)
e. (0,-5)
(1, - 2) and (5,10).....we can find the slope of a line connecttng these points thusly :
[ 10 - - 2 ] / [ 5 - 1 ] = 12 / 4 = 3
The equation of the said line is :
y = 3 ( x - 5) + 10
y = 3x - 15 + 10
y = 3x - 5 where this line crosses the y axis, x = 0....so
y = 3(0) - 5 = 0 - 5 = -5
So.....the line crosses the y axis at ( 0, - 5)
Here's a graph : https://www.desmos.com/calculator/eearzhfvuk
To answer the question, first figure out the equaton of the line. To do that first find the slope. The formula for the slope of a line is
m=y2−y1x2−x1 where m = slope, y2 = y-coordinate in the second point, y1 = y-coordinate in the first point, x2 = x-coordinate in the second point, and x1 = x-coordintate in the first point.
m=y2−y1x2−x1
m = ?
y2 = 10
y1 = -2
x2 = 5
x1 = 1
m=10−(−2)5−1
m=10+25−1
m=125−1
m=124
m=31
m=3
Now that we know that the slope of the line is 3, put that in the equation for a line. The equation for a line is
y=mx+b where y = y-coordinate, m = slope, x = x-coordinate, and b = y intercept (where line crosses the y axis). Take one of the points and susitute x and y in the equation so we can solve for b.
y=mx+b
y = 10
m = 3
x = 5
b = ?
10=3×5+b
10=15+b
10−15=15+b−15
−5=15+b−15
−5=b−0
−5=b
b=−5
Now fill in what you know leaving y and x as y and x.
y=3x−5
To figure out at which point the line crosses the y-axis, subsitute x for 0 and solve for x.
y=3x−5
y=3×0−5
y=0−5
y=−5
The point that the line crosses the y-axis is at point (0,−5) which means that the answer is neither a, b, c, or d.