The problem with equation (9) is that the
coefficients of and are not of the same
order of magnitude in t, as . A better choice of the
second variable y when passing from the second-order equation (1) to
an associated linear system (2) will remedy this.
are not of the same
order of magnitude in t, as 
. A better choice of the
second variable y when passing from the second-order equation (1) to
an associated linear system (2) will remedy this.