Go to your TV's settings menu and look for the Display or Picture section. Look for the Resolution or Screen Resolution option and check if it says 3840 x 2160 or UHD.
If your TV's resolution is set to 3840 x 2160, then it is running at 4K resolution. Additionally, you can check the packaging box or the user manual that came with your TV to see if it mentions 4K or UHD.
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Alternatively, you can check the TV's specifications online or look for reviews that mention the TV's resolution.
It's important to note that even if your TV is capable of displaying 4K resolution, the content you're watching must also be available in 4K in order to take full advantage of the higher resolution.