Question 864338
Let {{{u=s^2}}}
{{{u^2-11u+28=0}}}
{{{(u-4)(u-7)=0}}}
Two u solutions:
{{{u-4=0}}}
{{{u=4}}}
{{{s^2=4}}}
{{{s=0 +- 2}}}
.
.
{{{u-7=0}}}
{{{u=7}}}
{{{s^2=7}}}
{{{s= 0 +- sqrt(7)}}}