Answer: Â [tex]\bold{\dfrac{1}{2}(a-b)}[/tex]
Step-by-step explanation:
"half" means  [tex]\dfrac{1}{2}[/tex]
"of" means multiply
"difference" means subtract
half    of    the difference between a and b
 [tex]\dfrac{1}{2}[/tex]      ×    (                     a  -   b )
[tex]\large\boxed{\dfrac{1}{2}(a-b)}[/tex]