Instructions
Look at the beginning shape. You have four connected triangles, looking like four of six slices of pizza. The missing slices are the top one and the one directly to the left of the top one.
Pick up the matchstick that represents the crust of the bottom pizza slice. Place it in the shape where the top pizza crust would be.
Remove the matchstick that represents the crust of the upper right pizza crust. Place it on the shape to complete the top pizza slice, representing the left side of the slice of pizza.