What equation is the straight line passing through the points A (7; 19) and B (9:15).

General view of the equation of the straight line: y = kx + b.
Two values of x and y are known. To find the values of k and b, we compose a system of equations:
19 = 7k + b;

15 = 9k + b;

Express b from the first equation and substitute it into the second:
b = 19 – 7k;

15 = 9k + 19 – 7k;

9k – 7k = 15 – 19;

2k = -4;

k = -4 / 2;

k = -2;

If k = -1, then b = 19 – 7k = 19 + 14 = 33;

Answer: the equation of the straight line is: y = -2k + 33.