Whenever I see an expression like this, f(x)=-5x+6, how do I know if it is a function? Thank you.
A function crosses a vertical line only once. For example, if you sketched
a y parobla which opens upward or downward; a vertical line would cross it at only one point. Therefore the y parabola is a functin.
If you drew an x-parabola and drew a
vertical line through it, The line
would intersect it twice. Therefore, an x-parabola is NOT a function.
An x-parabola opens to the left or right.