In an xy-coordinate plane, a line is defined by y = kx + 1. If (1, b), (a, 4), and (a, b+1) are three points on the line, where a and b are unknown, then k = ?
Choose one:
A) 1/2
B) 1
C) 3/2
D) 2
E) 5/2
b=k+1...(1)   b+1=ak+1...(2)   4=ak+1...(3)   Taking (2) and (3)   4=b+1   b=3   Taking (1)   3=k+1   k=2   Answer : 2
<result>D</result>
In an xy-coordinate plane, a line is defined by y = kx + 1. If (1, b), (a, 4), and (a, b+1) are three points on the line, where a and b are unknown, then k = ?