Let and . Which is greater?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. x < y.
(a + b)2 = a2 + b2 + 2ab
x2 = 2 + 5 + 2√10 = 7 + 2√10
y2 = 7 + 3 + 2√21 = 10 + 2√21
x2 - y2 = (7 + 2√10) - (10 + 2√21) = -3 + 2(√10 - √21)
Since √10 < √21, √10 - √21 < 0
So x2 - y2 < 0
⇒ x2 < y2
Since x, y > 0, then x < y