@ Shubhanshu
x^2 is always positive independent of sign of x the only thing here is bx as the roots are given positive if we replace x with |x| we will get negative value's of x also as the root because they are producing the same bx;
ex: (x-2)(x-3)=0 has root 2,3 which are positive.
now x^2 -5x+6=0 put mod on x we get
x^2-5|x|+6=0;
now x can take 2,3 and -2,-3 also as 2=|-2|