We are given :

Step 1: factor the part inside square root
The function given inside square root is of quadratic form.
So let us try to factorise it using AC method.
Here A*C = 4*25 = 100
so we have to find factors of 100 that add up to give -20.
the two factors are -10 and -10.
Rewriting the function :

=
=
=
Step 2:
Now we take square root of the factorised form

= 
Answer : (2x-5)
Hi, answer to your functional equation on the photo
The expanded form would be 100.000 +20.000+0.000+.500+.070+.001
The mode because it is the number that occurs more often but in this situation it would be most requested song.