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As any app for Confluence Cloud, you can install the app via the Confluence admin menu.
Log into your Confluence instance as an admin.
Click on “Apps > Manage apps” in the header menu.
Click on “Find new apps” on the right navigation.
Search for "KaTeX Math Expressions for Confluence" and select it.
Click on “Try it free” to install the app.
Usage
KaTeX Math Expressions for Confluence provides two macros to insert a math expression into any confluence page. To make use of the macro click the “Insert” / “+” Button in the edit mode and select one of the provided macro and add the expression as macro body. Use the macro "KaTeX (Inline)" to add the a math expression (inline) inside other content in your Confluence content and the macro "KaTeX (Block)" to insert it as block.
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Inline mode: The math expression is rendered as in one line