What does c represent

The formula of a straight line is `y=mx+c`

`c` is the point where the straight line crosses the `y` axis (`y` intercept).

Do we need to remember this?

No because it is so easy to work out

As follows:

`y=3x+1` is the formula of a straight line

If `x` is zero then:

`y=3times0+1`

`y=1`

The point where the slope hits the `y` axis is:

`x=0` and `y=1`

Likewise

The point where the line hits the `x` axis is

`y=3x+1`

If `y` is zero then:

`0=3x+1`

`3x=-1`

`x=-1/3`

The point where the line hits the `x` axis is:

 `x=-1/3` and `y=0`