Реши систему уравнений a=4 2a-b=21

To solve the system of equations, we can substitute the value of "a" from the first equation into the second equation:

a = 4

2(4) - b = 21

8 - b = 21

Now, let's isolate "b" by subtracting 8 from both sides:

-b = 21 - 8

-b = 13

To solve for "b," we can multiply both sides by -1 to change the sign:

b = -13

Therefore, the solution to the system of equations is a = 4 and b = -13.