Bunuel
In the xy-coordinate plane, Line J passes through points (−2,0) and (0,2). Line K passes through points (4,0) and (0,4). If point (j,k) is the point at which Line J and Line K intersect, which of the following is true of point (j,k)?
A. j>0 and k>0
B. j>0 and k<0
C. j<0 and k<0
D. j<0 and k>0
E. The product jk=0
I usually graph, but finding the equations for these lines is quick.
To find the intersection point for two lines: set the equations for y equal; solve for x (x-coordinate = j); then solve for y (y-coordinate = k)
Write the equation of the lines in slope-intercept form.
y = mx + b
m = slope =
\(\frac{rise}{run}=\frac{(y_2-y_1)}{(x_2-x_1)}\)b = y-intercept
Line J has slope
\(\frac{(0-2)}{(-2-0)}=\frac{-2}{-2} =\\
1\)From the prompt, when x=0,
b = 2 (y-intercept)
Line J: y = (1)x + 2
Line K's slope:
\(\frac{(4-0)}{(0-4)}=\frac{4}{-4} =\\
-1\)When x=0,
b = 4 (y-intercept)
Line K: y = (-1)x + 4
Set equations for y equal, solve for x
x + 2 = -x + 4
2x = 2
x = 1 (= the x-coordinate of the intersection point, =
j)
Plug x in to find y-coordinate:
y = 1 + 2
y = 3 (= y-coordinate of intersection point,
k)
Intersection point is (j,k) = (1,3)
Answer A