Expression 17: "a" equals StartFraction, "b" Subscript, 1 , Baseline minus "b" Subscript, 0 , Baseline Over StartNestedFraction, "p" Subscript, 5 , Baseline . "x" minus "p" Subscript, 4 , Baseline . "x" NestedOver "p" Subscript, 5 , Baseline . "y" minus "p" Subscript, 4 , Baseline . "y" , EndNestedFraction minus StartNestedFraction, "p" Subscript, 7 , Baseline . "x" minus "p" Subscript, 4 , Baseline . "x" NestedOver "p" Subscript, 7 , Baseline . "y" minus "p" Subscript, 4 , Baseline . "y" , EndNestedFraction , EndFractiona=b1−b0p5.x−p4.xp5.y−p4.y−p7.x−p4.xp7.y−p4.y