We can simplify the left-hand side of the equation first:
900 - 420 + 49 = 529
Now we can rewrite the equation as:
529 = (a - b)^2
To solve for a - b, we can take the square root of both sides:
√529 = |a - b|
Since the square root of a positive number is always positive, we can remove the absolute value:
a - b = ±23
Therefore, the value of a - b could be either positive 23 or negative 23.