是否 (whether or not)

The paperwork version of is or isn't是不是shì bú shì

• whether (or not)是否shì fǒu + Verb / Adj = "whether (or not)" — a formal is or isn't是不是shì bú shì.
• Excuse me, may I ask...?请问qǐng wènyou (polite)您nínwhether (or not)是否shì fǒusatisfied满意mǎn yì？ = "may I ask whether you're satisfied?"
• whether (or not)是否shì fǒu embeds a yes/no question inside a sentence.

whether (or not)是否shì fǒu + Verb / Adjective

• whether (or not)是否shì fǒu = "whether or not", in a formal register.

please请qǐngconfirm确认què rènyou您nínwhether是否shì fǒuagree同意tóng yì。

• whether (or not)是否shì fǒuto agree同意tóng yì = "whether (you) agree."

Recap

Read the full reference: HSK 6 grammar — Particles.