KVPY SX SB Exam 2013 Question Paper

Question : 4 of 120

Marks: +1, -0

If a, b are positive real numbers such that the lines ax + 9y = 5 and 4x + by = 3 are parallel, then the least possible value of a + b is

Solution:

a/4=9/b⇒ab=36

using AM ≥ G.M

{a+b}/2 ≥ √{ab}

⇒a+b ≥ 12

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