Amodel used for the yield y of an agricultural crop as a function of the nitrogen level n in the soil (measured in appropriate units) is y = kn 9 + n2 where k is a positive constant. what nitrogen level gives the best yield?

The Nitrogen level that will give the best yield is ; 3

The correct written function/model is ;

To determine the best yield we will have to determine the maximum yield of the model above.  

Maximum yield is ( y' = 0 )

Determine y' ( first derivative ) using the quotient rule

 = 0

Resolving the rule above

  = 0   given that K is a positive constant

Express the numerator as  = 0

∴

factoring the equation above

(3 - N) (3 + N) = 0     given that  k ≠ 0 and is positive value

Therefore the Nitrogen levels ( N ) = 3  ( we take only the positive value )

Hence we can conclude that The Nitrogen level that will give the best yield is ; 3

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Explanation:

The model written correctly is:

This is a mathematical question, instead of a chemistry question, and you should use calculus to find the nitrogen level that gives the best yield, since this is an optimization problem.

The best yield is the maximum yield, and the maximum, provided that it exists, is found using the first derivative and making it equal to zero: Y' = 0

To find Y' you must use the quotient rule.

Now make Y' = 0

         9k - kN² = 0

         9 - N² = 0 ⇒ (3 - N) (3 + N) = 0

         ⇒ 3 - N = 0 or 3 + N = 0 ⇒ N = 3 or N = -3.

Since N is nitrogen level, it cannot be negative and the only valid answer is N = 3.

You can prove that it is a maximum (instead of a minimum) finding the second derivative or testing some points around 3 (e.g. 2.5 and 3.5).