Question

What is the equation of a line that goes through `(7, -7)` and has a slope of `-3`?

Answer 1

You use standard form of `y=mx+c` and substitute in the given values to find the value of c

`y =(-3)x+14`

Explanation:

Using `y=mx+c` and universal notation of `(x,y)`

Let `y= -7`
Let `x=7`
Let `m=-3color(white)(xxx)` (this is fixed. It does not change!)

Giving:

`-7=(-3)(7) +c`

`-7 = -21+c`

Add +21 to both sides:

`-7 +21 = -21+21+c`

`14=0+c`

`c=14`

So the full equation of the line is:

`y =(-3)x+14`