Explanation

Given:

a^2 + b^2 = 8 ... (Equation 1)

(a - b)^2 = 4

Expanding the left side of the equation: a^2 - 2ab + b^2 = 4

Now, substitute Equation 1 into this equation: 8 - 2ab = 4

Subtract 8 from both sides: -2ab = -4

Divide both sides by -2: ab = 2

So, the value of ab is 2.