You can do this by assigning different Sheet Styles to the respective sheet.
To create a sheet style with landscape orientation:
Hit F11 to open the "
Styles and Formatting
" window (it may be already visible and docked);Switch from "
Cell Style
" to "Sheet Styles
";Right-click and select "
New
" (there's only this option);In the new Sheet Style properties, assign a name (for example, "
Landscape
"), and on the "Page
" tab, set the Orientation to "Landscape
";Hit OK. Now, there's your new sheet style in the sheet styles list.
Select the sheet that should have landscape orientation, and double-click on the new page style entry in the "
Styles and Formatting
" window to apply it to the current sheet.
That's it.