This is a bad way to say it:
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(x+1)=-1 as a zero.
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Just say, either x+1 is a factor of f; or say that -1 is a zero of f.
-1 | 2 -4 -5 1
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| -2 6 -1
|__________________________
2 -6 1 0
and next yhou want to factorize or find zeros of the quadratic factor.
Zeros for the quadratic factor
-------the two other real but irrational roots. (zeros)