#s = int_1^3 \ sqrt ( 1 + (y')^2 ) \ \ dx#
#s = int_1^3 \ sqrt ( 1 + (x^2/4 - 1/x^2)^2 ) \ \ dx#
# = int_1^3 \ sqrt ( 1 + x^4/16 - 1/2 + 1/x^4) \ \ dx#
# = int_1^3 \ sqrt ( x^4/16 + 1/2 + 1/x^4) \ \ dx#
# = int_1^3 \ sqrt ( (x^2/4 + 1/x^2)^2 ) \ \ dx#
# = (\ x^3/(12) - 1/x )_1^3 #
# = ( 27/(12) - 1/3 ) - ( 1/(12) - 1 ) = 17/6 #