The correct value of this algebraic expression is -1/16
Given the expression, [tex]\large \sf \dfrac{-b}{2a}[/tex], let's just: change the letters to the numbers and then perform the given operations.
*Equal signs will be positive ⇒ (-) (-)= + & (+) (+) = +
*Different signs will be negative ⇒ (-) (+) = - & (+) (-) = -
[tex]\\\large \sf \dfrac{-b}{2a} , \ a=-8 \ , \ b=-1[/tex]
[tex]\large \sf \dfrac{-(-1)}{2 \cdot (-8)}[/tex]
[tex]\large \sf \dfrac{1}{2 \cdot (-8)}[/tex]
[tex]\large \sf \dfrac{1}{-16}[/tex]
[tex]\blue{\boxed{\large \sf -\dfrac{1}{16} }}\\[/tex]
Therefore, the final answer to this simplification will be -1/16