What is 5x-y = - 1 in function form?

If by function form you're referencing a y = equation then this is how you do it.

You want the y variable to be alone on its own side, so our first step is to subtract that ugly 5x from the left side.

That gives you - y=-5x-1

Now, we never want the y to be negative so we fix this by multiplying both sides by negative one which will cancel out that negative.

We are then left with y=5x+1