How to set direct proportionality by the formula if its graph passes through the point M (0.5; -0.25).

Direct proportionality is given by a formula of the form y = kx. If a point is known, in this case it is a point M (0.5; – 0.25), then this means that we know the coordinates x and y. Knowing these coordinates, we can substitute their values ​​into the formula, and, having solved the resulting equation, find the value of the coefficient k.

In recording the coordinates of the point O (x; y), the x coordinate is written in the first place, the y coordinate in the second place. This means that we have x = 0.5, y = – 0.25.

– 0.25 = k * 0.5;

k = – 0.25: 0.5;

k = – 0.5.

Having found the coefficient k, we write the equation that sets the direct proportionality passing through the point M (0.5; – 0.25). We get the equation:

y = – 0.5x.