GATE 2011 CS (CS1) – Question 28
Let $R=E[X^2]-(E[X])^2$. Which always holds?
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Correct answer: (C) R≥0
Explanation
This quantity is variance: $R=E[(X-E[X])^2]$. A square is nonnegative, so its expectation is nonnegative whenever defined. R may be zero for a constant variable, excluding strict positivity. Thus C.