equation is gone

Have you been using MathType, or used MathType with this Document on another Mac, and now either do not have MathType installed, a compatible version of MathType installed, or did not start MathType prior to launching Pages v8.1? By default, whether in Page layout, or word processing mode, or regardless of the chosen template, the equation menu item should show on that Insert toolbar menu. Does it show as active on the regular Insert menu? I added the keyboard shortcut in the following image:

In Pages Preferences : General, have you selected Equations: [√] Insert equations with MathType? If MathType is not installed, then this will be grayed out.

What the hosting software blocked me from originally posting, and supercedes the partial post:

One has the choice of using the built-in Pages equation editor, or with a compatible version of MathType installed, that product. The latter is enabled through an optional Equations checkbox in Pages Preferences : General panel. If choosing to use MathType, that product must be launched before you launch Pages, and it must be installed on every Mac where you wish to open a Pages document containing MathType.

In Pages Preferences : General, have you selected Equations: [√] Insert equations with MathType? If MathType is not installed, then this will be grayed out, which is the default.

Without prior MathType usage, whether in Page layout, or word processing mode, or regardless of the chosen template, the equation menu item should appear as active, on that Insert toolbar item menu, and on the main menu bar Insert menu — as shown below with my added keyboard shortcut:

Any reinstallation of Pages was not going to resolve this issue.

hope someone can help!!!

Me too, but I suspect it's going to take more information about the issue than what you've provided so far.

What version of Pages? (Pages menu > About Pages)

Is macOS 10.14 (High Sierra) correct for the version of macOS you are using? (Apple menu > About this Mac)

From where is the equation missing? When was it last 'there"?

What user actions preceded the disappearance?

Have there been any recent updates or upgrades to your machine?

Regards,

Barry