Which of the following expressions is positive for any value of a:

Question

a^2+4, (a+8)^2, 5a^2+2, a+13, (a−4)^2+4, (a+1)^2−1

Answer 1

since a^2 ≥ 0, a^2+4 ≥ 4 so it is always positive
(a+8)^2 = 0 if a+8 = 0, so it is not always positive
Now do the others in like wise