Oh, boy!!!! A word problem!
Let's see. If the pan is 9" across, then its radius, and each cut side of a piece, is 4.5".
The widest part of the cut piece is 3", which is a chord of the pie circle.
Consider the cut piece to be composed of two right triangles, back to back, with their adjoining right angles at the center of the chord.
Then, each triangle has one side (the hypoteneuse) of 4.5" and the side opposite the central angle of 1.5".
The sine of this ratio, 1.5/4.5 or 1/3, is approximately 19.47 degrees.
Since the slice is made up of two such triangles, its included angle is 38.94 degrees.
Therefore, the entire pie would consist of 360/38.94 slices of this size, or about 9.244 slices.
Now, if you remove one slice of this size from the whole pie, the number of pieces which remain is,
ummmm,
one.