Question

If 16s^2 + 80s + c is a perfect square trinomial, what is c?

100

400

800

1,600

none of the answer choices

Answer 1

We want 16s^2 + 80s + c = (as + b)^2 = a^2 s^2 + 2ab s + b^2. Since a^2 = 16, take a = 4, then 2ab = 80 → 8b = 80 → b = 10. So c = b^2 = 100.

Answer: 100.