Please help! i do not understand !

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?

Cd is the perpendicular bisector of both xy and st, and cy=20. find xy.

Carl is hanging pictures in his home. there is a space on a wall that has a width of 4 feet. carl has pictures with different widths. which picture width would fit in the space on the wall? a. 46 inches b. 60 inches c. 50 inches d. 54 inches