as you can see above... notice the middle term, in a perfect square trinomial, the middle term is, 2 times the guy on the left, without the exponent, and times the guy on the right
so.. .what we have here ... let's see yours is
so.. we have a missing guy there, the guy on the right hmm what the dickens would that be anyway?
well... let us use the middle guy
aha ... there's our guy on the right.... so now we know is 1/5
now... let us call or very good friend Mr Zero, 0
if we "add" whatever, we also have to "subtract" whatever, since all we're really doing is, borrowing from 0
thus