One thing that keeps coming up in artificial grammar studies (in which people are taught bits of made-up languages) is that adults are much better at learning them than kids. Yet we know that if you wait 20 years, people who started learning a real language as a kid do much better than those who started as adults. This might mean the artificial grammar studies aren't ecologically valid, but I think it's also the case that in real-life second-language acquisition, adults start out ahead of kids. Whatever makes kids better language learners seems to be something that happens after the first few weeks/months of learning.
How to calculate trigonometry functions
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