Find a non-zero real number that satisfies the equation above.
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y 2 + y 3 + … + y 6 0 + … + y 9 9 = 0 y 2 ( 1 + y + y 2 + y 3 + … + y 9 4 + y 9 5 + y 9 6 + y 9 7 ) = 0 y 2 ( 1 ( y + 1 ) + y 2 ( y + 1 ) + … + y 9 4 ( y + 1 ) + y 9 6 ( y + 1 ) ) = 0 y 2 ( y + 1 ) ( 1 + y 2 + … + y 9 4 + y 9 6 ) = 0
The first factor:
y 2 = 0 ⟹ y = 0
This is not non-zero, so we ignore it.
The second factor:
y + 1 = 0 ⟹ y = − 1
The third factor
1 + y 2 + … + y 9 4 + y 9 6 = 0
Notice that for even positive integers of n , y n ≥ 0 for all real values of y
This implies that y 2 ≥ 0 , … , y 9 4 ≥ 0 , y 9 6 ≥ 0
Therefore,
y 2 + … + y 9 4 + y 9 6 ≥ 0 1 + y 2 + … + y 9 4 + y 9 6 ≥ 1
From this, we can conclude that the third factor has no real roots.
Therefore, the only non-zero real solution is y = − 1