You know that a perfect square trinomial is given by square of first term, twice the product of first and last terms and square of second term
So we have x^2 that is square of x, 2x that is twice the product of x*1, the second term shoulf be 1, that is square of 1
So your answer would be 1
If you try (x+1)^2 = x^2+2x+1