Explanation

The equation x + a + b = abx/(ab + ax + bx) has roots α, β. Cross-multiplying gives (x+a+b)(ab + x(a+b)) = abx, which expands to x²(a+b) + x(a+b)² + ab(a+b) = 0. Dividing by (a+b) yields x² + (a+b)x + ab = 0, so α + β = −(a+b) and αβ = ab. Hence αβ + α + β = ab − a − b, option (b).