How do i improve and strengthen my brain? i do math and science problems a lot but are there any vitamins or anything i can take to expand my brain?

Maybe: The brain requires proper nutrition to function at it's best. The 2 things that are most likely to be deficient are vitamin d and omega 3 essential fatty acids which are usually obtained from eating cold water fish or fish oil supplements. B vitamins are also important for the brain and so is exercise.

Not the way you mean: Evidence is accumulating that physical exercise is more important than mental exercise in preserving cognitive function throughout life. This whole big thing with keeping your brain healthy is WAY overblown. Just don't worry about it. You're 19 years old, for heaven's sake. Worry more about overall fitness. A healthy body promotes a healthy mind.