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Mathematics
Problem
Given positive real numbers
a
a
a
and
b
b
b
satisfying
a
b
=
81
ab = 81
ab
=
81
, prove that
a
+
b
≥
18
a + b \ge 18
a
+
b
≥
18
and state the values of
a
a
a
and
b
b
b
for which equality holds.
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