Imaginary Unit
<p> </p><ol style="margin: 0px; padding: 0px 0px 0px 2.25em; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; color: rgb(34, 34, 34);"><li style="margin-top: 0px; margin-right: 0px; margin-bottom: inherit; margin-left: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;"><span class="ib-brac" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;">(</span><span class="ib-content" style="margin: 0px; padding: 0px; border: 0px; font-style: italic; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;"><a href="https://en.m.wiktionary.org/wiki/complex_analysis" title="complex analysis" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none; color: rgb(107, 75, 161);">complex analysis</a></span><span class="ib-brac" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;">)</span> A <a href="https://en.m.wiktionary.org/wiki/complex_number" title="complex number" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none; color: rgb(107, 75, 161);">complex number</a>, usually denoted with <i style="margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;">i</i>, that is defined by <span class="mwe-math-element" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none;"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; background: none; display: none; clip: rect(1px, 1px, 1px, 1px); overflow: hidden; position: absolute; width: 1px; height: 1px; opacity: 0;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle i{2}=-1}"><semantics><annotation encoding="application/x-tex">{\displaystyle i{2}=-1}</annotation></semantics></math></span><img width="0" height="0" class="mwe-math-fallback-image-inline image-lazy-loaded" alt="{\displaystyle i{2}=-1}" src="https://wikimedia.org/api/rest_v1/media/math/render/svg/88e98a401d352e5037d5043028e2d7f449e83fa6" srcset="" style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; line-height: inherit; font-family: inherit; vertical-align: middle; background: none; display: inline-block; animation: 0.3s ease-in 0s 1 normal none running fadeInImage; width: 7.926ex; height: 2.843ex;"></span></li></ol>