If you want to play it safe (or avoid killing the T. rex for the achievement), run into one of the caves along the right-hand wall of the valley. Don't pick the alcove nearest the entrance from the caves; it's too shallow, and the T. rex can easily reach Lara.
Instead, choose the ground-level opening just below the right side of the broken bridge.
Follow this passageway forward then left.
About halfway in you'll encounter another raptor (10). If you approach cautiously and get a pistol lock on it, you can back away while firing without being bitten.
When it's dead, continue to a wide opening higher in the valley wall.
Then just wait and blast the T. rex as it stomps by.
If it wanders off, you can dangle Lara from the edge to get its attention. Then pull up, turn around and continue firing.
Or, return along the tunnel to the first opening and try to shoot it from there.
DARK MODE: Even with brightness adjusted, dark images on a light background can be hard to see. May I suggest a reputable dark mode browser extension, such as Dark Reader? (Download only from trusted sites, like darkreader.org or your browser's web store.)
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