Which polynomial is the perfect square trinomial? and

See the attached

When you square the binomial (a -b), you get ...

... (a -b)² = a² -2ab +b²

That is, both the a² and b² terms have positive signs, and the middle term is twice the product of the roots of the squared terms.

The last two selections have negative signs on the constant, so cannot be perfect square trinomials.

The first selection has a middle term that is -ab, not -2ab, so it is not a perfect square trinomial, either.

The second selection is the correct one:

... 4a² -20a +25 = (2a +5)²

i just took the test, the correct answer is .. 31.5 in.