x and y are real numbers such that x , y > 0 , x y = 1 then calculate minimum value of x + y
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If we are using differentiation method, we are getting 2 & -2 as the extreme values of the equation, so why is 2 minimum ?
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Because it is given in the question that x and y both are greater than 0 , therefore x+y cannot be -2 and thus answer results in +2 .
Moreover we can only apply A.M>G.M when x and y both are positive numbers :)
x,y is greater than 1.so only positive number which can give result 1 is (1multiplied by 1).
so 1+1=2.
A product will achieve the minimum sum of two factors if these two factors are equal to each other. In the case of all positive numbers, this can be achieved with two equal positive or two equal negative factors. However, because this problem specifies that x , y > 0 , we only need to find the sum of two equal positive factors. In the case of 1 , these factors are 1 and 1 , and 1 + 1 = 2 .
This would be a great trick question if it weren't specified that x , y > 0 .
The only value of x and y is 1 because their product should be 1. 1 + 1 = 2
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Applying AM ≥ GM as x , y > 0 and positive,
2 x + y ≥ x y
⟹ 2 x + y ≥ 1 ∵ x y = 1
⟹ x + y ≥ 2
Minimum value of x + y is 2