can you show me how to factor this problem?

you need to use the following rule:

a^2 - b^2 = (a+b)(a-b)

in this case, a = y and b = sqrt(25) = 5

y^2 - 5^2 = ( y + 5) (y-5)

Both y^2 and 25 are perfect squares.

Since the 25 is negative, the correct factoring would be

(y - 5)(y + 5) = 0

If you wish to solve,

y = 5, -5

a^2 --b^2 = (a+b)(a--b)

Just following the above identity, a =y and b = 5

So, y^2 --5^2 = (y+5)(y--5)

Thus factorized.

y^2-25=0

y^2=25

square root 25

=y=5