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218 • Chapter 6: Examples from CalculusThe derivative, B1, of B is zero at a critical point.> B1 := diff( B, x );B1 := − 1 (x − π)540> sol := { solve( B1=0, x ) };sol := {π}At the critical point the error is> eval( B, x=sol[1] );0> critical := critical union { % };critical :={0, −0.01542298119 (4 − π) 6 , 0.07333000221 (2 − π) 6 }At the last boundary, ξ = x, the error is> B := eval( err, xi=x );B := 1720 (−sin(x) esin(x) + 16 cos(x) 2 e sin(x) − 15 sin(x) 2 e sin(x)+ 75 sin(x) cos(x) 2 e sin(x) − 20 cos(x) 4 e sin(x) − 15 sin(x) 3 e sin(x)+ 45 sin(x) 2 cos(x) 2 e sin(x) − 15 sin(x) cos(x) 4 e sin(x)+ cos(x) 6 e sin(x) )(x − π) 6Again, you need to find where the derivative is zero.> B1 := diff( B, x );