c > math > equation of a straight line

# Equation of a Straight Line

Any straight line can be written in the standard form: $$y=mx+c$$

The gradient, $m$ is given by the formula: $$m=\frac{y_2-y_1}{x_2-x_1}$$

The y-intercept, $c$ can be found by substituting the gradient and any of the points (in this case we use $(x_1,y_1)$) into the standard form of the line equation: $$y_1=mx_1+c$$ $$\therefore c=y_1-mx_1$$

The following code snippet shows how we can replicate this in C:

```
#include <stdio.h>
int main(){
// storing the points
double x1=-2.5,x2=0,y1=0,y2=5;
printf("Using the points (%g,%g) and (%g,%g)\n",x1,y1,x2,y2);
// calculating gradient
double gradient = (y2-y1)/(x2-x1);
printf("The gradient of the line is %g\n",gradient);
//calculating the y-intercept
double y_intercept = y1-gradient*x1;
printf("The y intercept is %g\n",y_intercept);
// displaying the final equation of the straight line
printf("Therefore the equation of the line is:\ny=%gx+%g",gradient,y_intercept);
return 0;
}
```

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**c/math/finding_the_equation_of_a_line_given_two_points.c**