Verified Answer :

i=√-1 and all the steps are there

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f(x) = x³ - 2x².

f(i) = i³ - 2i².

i = √-1.

i³ = (√-1)³ = √-1 √-1 √-1 = -1√-1 = -√-1 = -i

i² = (√-1)² = √-1
√-1  = -1

f(i) = i³ - 2i²  = -i - 2(-1) = -i + 2

f(i) = 2 - i