How do I get out of Chamber 17?

So I'm stuck in GLaDOS 17. I have put the cube on the button, connected the laser to its output, explored the back area of the room hoping for exits — but I could not find a way to reach the exit of the chamber.

How do I get out of here?

2 Answers

You need to drop the cube while standing on the platform. The platform will be down while the cube is blocking the beam.

1. block beam with the cube (on top of hard light)
2. step on the platform
3. make cube drop by redirecting the hard light
4. beam will activate the platform, which will get you to the exit, cube will open exit

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With pictures (for fun)

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