SOLUTION: a = 2+ sqare root of 3. to find a^2 +1/a^2

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Question 1046166: a = 2+ sqare root of 3. to find a^2 +1/a^2
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
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a = 2 + square root of 3. highlight%28cross%28to%29%29 Find a^2 +1/a^2.
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First let us prove this statement:


    If a = 2+%2B+sqrt%283%29, then 1%2Fa = 2+-+sqrt%283%29


Indeed,  %282+%2B+sqrt%283%29%29%2A%282+%2B+sqrt%283%29%29 = 2%5E2+-+%28sqrt%283%29%29%5E2 = 4 - 3 = 1,  so the statement is proved.


Next,  a%5E2 + 1%2Fa%5E2 = %28a+%2B+1%2Fa%29%5E2+-+2.   (*)


Notice that  a+%2B+1%2Fa = %282+%2B+sqrt%283%29%29 + %282-sqrt%283%29%29 = 4.


Therefore, we can continue (*) in this way:


a%5E2 + 1%2Fa%5E2 = %28a+%2B+1%2Fa%29%5E2+-+2 = 4%5E2+-+2 = 16 - 2 = 14.


Answer.  If  a = 2%2B+sqrt%283%29  then  a%5E2+%2B1%2Fa%5E2 = 14.