The straight line passes through the points A (2; 1) and B (0; 3) write the equation of the straight line AB.

1). Substitute the coordinates of point A (2; 1) into this equation. The abscissa x is written in the first place, the ordinate y is in the second.

x = 2; y = 1;

we obtain the equation 1 = 2k + b.

2) Substitute the coordinates of point B (0; 3).

x = 0; y = 3;

we get the equation 3 = 0 * k + b.

3) Combine the resulting equations into a system and solve it.

2k + b = 1; b = 3;

2k + 3 = 1; b = 3;

2k = 1 – 3; b = 3;

2k = -2; b = 3;

k = -2: 2; b = 3;

k = -1; b = 3.

Substitute the found coefficients k and b into the equation y = kx + b:

y = -1x + 3;

y = -x + 3.

Answer. y = -x + 3.