Salutare!
f : R → R
f(x) = 8 - x
f(1) × f(2) × ... × f(2020) = ?
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f(1) = 8 - 1 = 7
f(2) = 8 - 2 = 6
f(3) = 8 - 3 = 5
. . . . .
f(8) = 8 - 8 = 0
. . . . . .
f(2020) = 8 - 2020 = -2012
⇒ f(1) × f(2) × ... × f(2020) =
= f(1) × f(2) × ... × f(8) × ... × f(2020) =
= 7 × 6 × .... × 0 × ... × (-2012) = 0
