What are the coefficients a and b if it is known that a pair of numbers (-1, -2) is a solution

What are the coefficients a and b if it is known that a pair of numbers (-1, -2) is a solution to the system of equations 5x + ax = -1. by-4y = 5

We have a system: 5x + ax = – 1; by – 4y = 5;

From these conditions, we substitute x = – 1 into the first equation of the system and solve it:

When x = – 1; 5x + ax = – 1 will take the form:

– 5 – a = – 1; the terms with the unknown are grouped on one side of the equal sign, without the unknown – on the other:

a = 1 – 5 = – 4.

Further, from these conditions, we substitute y = – 2 into the second equation of the system and solve it:

When y = – 2; by – 4y = 5 becomes:

– 2b + 8 = 5; the terms with the unknown are grouped on one side of the equal sign, without the unknown – on the other:

2b = 8 – 5 = 3;

b = 3/2 = 1.5.