Hi @Work_kids_coding, the √ symbol means square root. "What is the square root of 25?" is the same as "What number multiplied by itself gives 25?" Since 5x5=25, the square root of 25 is 5. So √25 = 5
If you've never seen those calculator functions inside Edit mode before, you can find them by scrolling down with the Calculator menu:
And @Kiwicute2015 posted her very helpful project on sin and cos, and you can also check out this forum post on What are sin and cos?