The last one does not represent a function because for it to be a function none of the x’s can repeat and in the last one the 0 repeats.
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Answer:
x∈{-7√2, 7√2}
Step-by-step explanation:

Answer:
y = -0.07x2 + 3.07x
Step-by-step explanation:
For each plant we add, there is a decrease of 70 grams for all plants from the inicial value of 3 kg of beans.
So, for 2 plants, we have (3 - 0.07) * 2
For 3 plants, we have (3 - 2*0.07) * 3
For x plants, we have (3 - (x-1)*0.07) * x
So we can model the final result of the amount of beans 'y' with the equation:
y = (3 - (x-1)*0.07) * x
y = (3 - 0.07x + 0.07) * x
y = (3.07 - 0.07x) * x
y = -0.07x2 + 3.07x
(In this equation we have a = -0.07, b = 3.07 and c = 0)