Question

What is the equation in point-slope form of the line passing through (1, 9) and (−1, 11)?

Answer 1

use the point slope formula, y-y1=m(x-x1) to find the equation of the line.
y=-x+10

Answer 2

(1,9)(-1,11)
slope = (11 - 9) / (-1 - 1) = -2/2 = -1

there can be 2 answers for this...
y - y1 = m(x - x1)
(1,9)...x1 = 1 and y1 = 9
sub
y - 9 = -(x - 1) <== here is one answer

y - y1 = m(x - x1)
(-1,11)...x1 = -1 and y1 = 11
sub
y - 11 = -(x - (-1) =
y - 11 = -(x + 1) <== here is the other answer