format long
fzero(@f, -.7)

ans =

  -0.716353356220526

fzero(@f, -.25)

ans =

  -0.249030753806766

fzero(@f, .1)

ans =

  -0.017448261900619

fzero(@f, .42)

ans =

   0.453191551623393

fzero(@f, .98)

ans =

   0.978242301083763

fzero(@f, 2.5)

ans =

   2.511671398409057