Find the infimum and supremum of each of the following sets.
a) E = {x ∈ R : x2 + 2x = 3}
b) E = {x ∈ R : x2 - 2x + 3 > x2 and x > 0}
c) E = {p/q ∈ Q : p2 < 5q2 and p, q > 0}
d) E = {x ∈ R: x = 1 + (-l)n/n for n ∈ N}
e) E = {x ∈ R: x = l/n + (-1)n for n ∈ N}
f) E = {2-(-l)n/n2: n ∈ N}