Given 2 points, how do you calculate the equation of a straight line?

Remember that the equation of a straight line function is: ax+c. a= change of y/ change of x
The steps to follow are:1- find the gradient of the slope2- replace the equation by values coming from any of the 2 points
Example: 2 points (3;8) and (-1;3)Therefore: a= 3-8/-1-3 = 1.25Now: y= 1.25x + c
To find c: Replace value from any of the points: For instance: first point 3;8 where x=3 and y=88= 1.25 x 3 + cc= 8/ 3.75