No.
This is almost a perfect square trinomial, but it is not.
We can verify this by looking at the first two terms.
With only x^2 + 20x, we could complete the square to make this a perfect square trinomial by performing the following steps:
Divide the middle term by 2.
20 / 2 = 10
Square the quotient.
10^2 = 100.
Add 100 to both sides.
x^2 + 20x + 100 = 100
As the provided trinomial is x^2 + 20x - 100, it is not a perfect square trinomial.
