How do you determine if #2x+y=7# is a function?
A function is anything that can pass the vertical line test, or when for every "y" there is only one "x" value. Typically, all lines are functions.
2x+y=7 is a function because it is in the form of y=mx+b (slope-intercept form). If you rewrite the function, you should get y= -2x+7.