x 4 + a x 3 + b x 2 + c x + 1 x 4 + 2 a x 3 + 2 b x 2 + 2 c x + 1
Both the expressions above are perfect squares for some a , b , c > 0
Find a + b + c
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Yup. Just as I did it.
The best way to get the answer
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let x 4 + a x 3 + b x 2 + c x 2 + 1 = ( x 2 + α x + 1 ) 2 x 4 + a x 3 + b x 2 + c x 2 + 1 = x 4 + 2 α x 3 + ( α 2 + 2 ) x 2 + 2 α x + 1 we can say { a = c = 2 α b = α 2 + 2 = 4 a 2 + 2 let x 4 + 2 a x 3 + 2 b x 2 + 2 c x 2 + 1 = ( x 2 + β x + 1 ) 2 x 4 + 2 a x 3 + 2 b x 2 + 2 c x 2 + 1 = x 4 + 2 β x 3 + ( β 2 + 2 ) x 2 + 2 β x + 1 we can say that { a = β 2 b = β 2 + 2 = a 2 + 2 inserting b from the first expression, 2 ( 4 a 2 + 2 ) = a 2 + 2 ⟶ a = 2 and a + b + c = a + a + 4 a 2 + 2 = 2 + 2 + 4 4 + 2 = 7