Question Details

If x and y are positive real numbers satisfying x+y=102, then the minimum possible value of 2601(1+1x)(1+1y) is

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Correct Answer :

2704

Solution :

The correct answer is 2704.

We are given that x and y are positive real numbers with x + y = 102, and we need to find the minimum value of:

2601 (1+1x) (1+1y)

Step 1: Expand the expression inside.

First, let's expand the product (1+1x)(1+1y):

= 1 + 1x + 1y + 1xy

Combining the middle two fractions over a common denominator xy:

= 1 + x+y xy + 1xy = 1 + x+y+1 xy

Step 2: Substitute the constraint x + y = 102.

Replacing x + y with 102:

= 1 + 102+1 xy = 1 + 103xy

So the full expression becomes:

2601 ( 1 + 103xy ) = 2601 + 2601×103 xy

Step 3: Determine what minimizes the expression.

Since 2601 is a constant and 103 is positive, the term 2601×103xy decreases as xy increases. Therefore, to minimize the entire expression, we need to maximize the product xy.

Step 4: Maximize xy using the AM-GM Inequality.

The AM-GM inequality states that for positive real numbers:

x+y 2 xy

Squaring both sides:

xy (x+y2) 2 = (1022) 2 = 512 = 2601

Equality holds when x = y = 51. So the maximum value of xy is 2601.

Step 5: Compute the minimum value.

Substituting xy = 2601 into the expression:

2601 + 2601×103 2601 = 2601 + 103 = 2704

Elegant Observation: Notice that 2601=512 and 2704=522. The minimum value is the perfect square of (51 + 1) = 52, which is a beautiful result!

Verification: At x = y = 51:
2601 (1+151) (1+151) = 2601 × (5251) 2 = 2601 × 27042601 = 2704

Therefore, the minimum possible value is 2704.

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