Let
A (x1,y1)-------> (1,5)
B (x2,y2)------> (5,10)
C (x3,y3)------> (9,15)
D (x4,y4)------> (13,20)
find the slope
AB
m=(10-5)/(5-1)-----> m=5/4
find the slope
CB
m=(15-10)/(9-5)-----> m=5/4
find the slope
DC
m=(20-15)/(13-9)-----> m=5/4
so
the relationship shown is linear
to model the data with an equation find the equation of a line
with m=5/4 and point A (1,5)
y-y1=m*(x-x1)-----> y-5=(5/4)*(x-1)----> y=1.25x-1.25+5-----> y=1.25x+3.75
the equation to model data is
y=1.25x+3.75
see the attached figure
