RRB Technician Grade I 19 Dec 2024 Shift 2 Paper

Concept:Use the algebraic identity $(x + a)(x + b) = x^2 + (a + b)x + ab$ to expand the product of two linear binomials.Explanation:Compare $(x - 9)(x + 8)$ with the standard form $(x + a)(x + b)$.Here, $a = -9$ and $b = 8$.Sum of the constants: $a + b = -9 + 8 = -1$.Product of the constants: $a \times b = (-9) \times 8 = -72$.Substitute these values into the identity.$(x - 9)(x + 8) = x^2 + (-1)x + (-72)$.Simplify the expression to get $x^2 - x - 72$.This matches option B exactly.Answer:The product of $(x - 9)$ and $(x + 8)$ is $x^2 - x - 72$.Therefore, the correct option is B.