Question

y=5x-4 is this a function

Answer 1

yes
if you graph it, you'll get a straight line
all straight lines are functions except if they are vertical.

Answer 2

the equation is a function if for each value of x there is only 1 value of y. From a graphical standpoint, if at any point you can draw a vertical line on the graph and cross the graph of the equation twice, it is not a function.

\[y=x^2\] is a function, because for each value of \(x\), there is only one value of \(y\). \[x=y^2\] has the same shape, rotated 90 degrees, but is not a function, because for many values of \(x\), there are two values of \(y\).