Specify direct proportionality by the formula if it is known that the graph passes through point A (2; 9) B (3; -7).

Direct proportionality is a special case of a linear function. The linear function is given by a formula of the form y = kx + b, and direct proportionality is given by y = kx. Linear proportionality plot is a straight line passing through the origin.

1) A (2; 9); x = 2; y = 9;

substitute the values of the abscissa and ordinate into the equation of direct proportionality and find the coefficient k;

9 = 2k;

k = 9: 2;

k = 4.5.

the equation will be y = 4.5x.

2) B (3; -7); x = 3; y = -7;

-7 = 3k;

k = -7: 3;

y = -2 1/3;

we get the equation y = -2 1/3 x.