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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
No problem, you're welcome.
That means, the derivative of x^2 should be noted as 2x^1 instead of 2x. I think you didn't get that part.
Your code returns 2x^2 instead. That's why it is invalid.
It passes, why do you say it won't? Have you tried it? Your code is wrong and it passed because random tests didn't generate a test with exponent = 2.