Not too sure how to go about this if you do answer please explain how you got your answer

1. what is the phythaforean theorem? 2.what do we use it for? 1.what is the distance formula ? 2.what do we use it for?

Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

Dylan and dusty plan to take weekly surfing lessons together. if the 2-hour lessons are $20 per person and they plan to spend $100 each on new surfboards, what is the maximum number of lessons the two can take if the total amount spent for lessons and surfboards is at most $480?