<math display='block'> <mmlrow> <mmlsub> <mmli>V</mi> <mmlrow> <mmli>t</mi><mmli>E</mi><mmli>F</mi> </mrow> </msub> <mmlo>=</mo><mmlo stretchy='false'>(</mo><mmli>r</mi><mmlo>&#x2212;</mo><mmli>b</mi><mmlo>&#x2212;</mo><mmli>l</mi><mmlo stretchy='false'>)</mo><mmli>&#x03C9;</mi><mmli>cos</mi><mmli>&#x03B8;</mi> </mrow> </math>