They are opposites. since |-3| has the lines around it, this represents absolute value, which is not positive or negative but how far away the value is from 0. the plain -3 remains the same. |-3| is 3, because it is 3 units away from 0 on the number line.
A second degree polynomial function has the general form:

, where

.
The leading coefficient is a, so we have a=-1.
5 is a double root means that :
i) f(5)=0,
ii) the discriminant D is 0, where

.
Substituting x=5, we have
f(5)=a(5)^2+b(5)+c,
and since f(5)=0, and a is -1 we have:
0=-25+5b+c
thus c=25-5b.
By ii)

.
Substituting a with -1 and c with 25-5b we have:
Finally we find c: c=25-5b=25-50=-25
Thus the function is

Remark: It is also possible to solve the problem by considering the form

directly.
In general, if a quadratic function has leading coefficient a, and has a root r of multiplicity 2, then its form is
8/28=4/14=2/7
2/7 is simplest form
Not 100% sure but hopefully this helps