This is a very complex shadow. It will require some work.
This is the direction of the light source so the shadow would be cast to the right.
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First make sure you duplicate the original.
You need to make a selection of the tee to the left.
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On a layer below the double tee's, fill the selection with black. Name this layer "Shadow".
With the shadow layer selected/highlighted, enter free transform, right click and choose 'distort'.
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Now manipulate the shadow into position.
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When your done click the checkmark or hit enter to accept the changes.
Next, on the shadow layer, I used the Polygonal Lasso Tool to make a small triangle representing the second tee's skinny little shadow. Fill the selection with black.
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Next, lower the opacity of the shadow layer.
Add a Gaussian Blur.
You can also add a layer mask and use the Gradient Tool to soften the top of the shadow to simulate how a shadow fades as it becomes diffused with light as it gets further away from its source.
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