Please help me out with this 25 points should be enough, you don’t have to but if you want to help me out then thank you

A20? -foot ladder is placed against a vertical wall of a? building, with the bottom of the ladder standing on level ground 19 feet from the base of the building. how high up the wall does the ladder? reach?

Find the center and the radius of the circle with the equation: x^2-2x+y^2+4y+1=0?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?