Final answer:
The value of ab cannot be found as the value of a is not real.
Step-by-step explanation:
In this case, we have a system of equations:
a - b = 1
a² + 62 = 13
4a²b = 72
From the second equation, we can solve for a:
a² = 13 - 62
a² = -49
a = ± √(-49)
Since we can't take the square root of a negative number, the value of a is not real.
Therefore, we cannot find the value of ab.