Which of the following is equal to –1?

The correct answer is ( i^2 ).

Explanation: The imaginary unit ( i ) is defined as ( i = sqrt{-1} ). Here are the powers of ( i ):

– ( i^1 = i )

– ( i^2 = -1 )

– ( i^3 = -i ) (which is ( i^2 cdot i = -1 cdot i ))

– ( i^4 = 1 ) (which is ( i^2 cdot i^2 = -1 cdot -1 ))

Among the options, ( i^2 = -1 ) is the correct answer. Keep studying, and if you have more questions, feel free to ask!