Question

What equation represents a line that passes through (2, -1) and has a slope of 4

Answer 1

y=mx+c is the basic equation of a straight line, where m is the gradient (slope) and c is a constant.
Since you already know the gradient (4) and you have been given two points (2, -1) you just need to find c. for the equation. To do this, substitute x and y in the equation from the point you've been given and substitute the gradient to find c.
So;
-1=4*2 +c
Rearrange to find c.
-1 = 8 +c
-9 = c
Therefore the equation of the line is:
y=4x - 9