The expression i² equals -1.
In mathematics, ‘i’ is known as the imaginary unit. It is defined as the square root of -1, which means when you square ‘i’, you multiply it by itself: i × i. Since the square root of a negative number cannot be represented on the real number line, mathematicians have created this concept of imaginary numbers. Therefore, i² = -1 is a fundamental aspect of complex numbers, which are numbers that have both a real part and an imaginary part. This relationship between ‘i’ and negative numbers is crucial for understanding many concepts in advanced mathematics, engineering, and physics.