If two variables \(x\) and \(y\) and \(x>0 . x y=1\) then minimum value of \(\mathrm{x}+\mathrm{y}\) is (a) 1 (b) 2 (c) \(2(1 / 2)\) (d) \(3(1 / 3)\)

Short Answer

Expert verified
The minimum value of \(x+y\) under the given constraints is (b) 2.

Step by step solution

01

Write down given constraints and expression to minimize

We are given the constraints x > 0 and xy = 1, and we want to find the minimum value of x + y.
02

Apply AM-GM inequality to x and y

The Arithmetic Mean (AM) of x and y is given by \(\frac{x+y}{2}\). The Geometric Mean (GM) of x and y is given by \(\sqrt{xy}\). According to AM-GM inequality, we have: \[\frac{x+y}{2} \geq \sqrt{xy}\]
03

Use the given constraint xy = 1

Since we have xy = 1, we can substitute this value into the inequality from Step 2: \[\frac{x+y}{2} \geq \sqrt{1}\]
04

Simplify the inequality and solve for x + y

The inequality from Step 3 simplifies to: \[\frac{x+y}{2} \geq 1\] Now, multiply both sides of the inequality by 2 to isolate x + y: \[x+y \geq 2\]
05

Identify the minimum value of x + y

From the inequality \(x+y \geq 2\), we can conclude that the minimum value of x + y is 2. So, the correct answer is: (b) 2

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