If x 1 and x 2 are the roots of the equation x 2 − 8 x + 1 1 = 0 , determine the value of
x 1 3 + x 1 2 + x 1 + x 2 3 + x 2 2 + x 2
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Is this known as transformation of roots? It's quite brilliant!
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Glad that you like it again.
No. That's like if f ( x ) = 0 has roots a and b , then f ( 1 / x ) = 0 has roots 1 / a and b .
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Given that:
x 2 − 8 x + 1 1 ⟹ x 2 x 3 ⟹ x 3 + x 2 + x = 0 = 8 x − 1 1 = 8 x 2 − 1 1 x = 8 ( 8 x − 1 1 ) − 1 1 x = 5 3 x − 8 8 = 6 2 x − 9 9
Since x 1 and x 2 are the roots of x 2 − 8 x + 1 1 , the sum:
S = x 1 3 + x 1 2 + x 1 + x 2 3 + x 2 2 + x 2 = 6 2 x 1 − 9 9 + 6 2 x 2 − 9 9 = 6 2 ( x 1 + x 2 ) − 1 9 8 = 6 2 ( 8 ) − 1 9 8 = 2 9 8 By Vieta’s formula x 1 + x 2 = 8
Reference: Vieta's formula