one-to-one, meaning each output only has one input
many-to-one meaning some outputs can have more that one input, but all inputs only have one output
So, That pic is cramped, don't even know what functions are being referenced but
from the a, b, c, d relation
It is not a function because some inputs have more that one output, which fails our man-to-one rule
From the equations
-3x = 15 is not a function, because it only has one input but more than one output breaking rule 1
2y=10 is a function because every input x has only one output y, it is many-to-one
3x-0.25y=3 is a function, it is one to one
From the graph
the line is a function, since it is many-to-one
From the points
the x coordinate is the input, not points (2,6) and (2,3) have the same input for two outputs, breaking rule 2, that each input should have only one output. So the points are not a function
