Write the equation of the straight line through the origin and point B (-2; 4).

The origin of coordinates, that is, point O has coordinates O (0; 0).
An equation of a straight line passing through points with coordinates (x0; y0) and (x1; y1) is compiled according to the formula:
(x – x0) / (x1 – x0) = (y – y0) / (y1 – y0).
Therefore, we compose the equation of the straight line passing through these points with coordinates O (0; 0) and B (-2; 4) and get:
(x – 0) / (- 2 – 0) = (y – 0) / (4 – 0);
x / -2 = y / 4.
Answer: -x / 2 = y / 4.