In an AP, if the 12th term is -13 and the sum of its first four terms is 24. Find the sun of its
first 20 terms

How to choose the sign of the radical in the denominator of the formula for the distance from a point to a line.

Kayla wants to find the width, ab, of a river. she walks along the edge of the river 65 ft and marks point c. then she walks 25 ft further and marks point d. she turns 90° and walks until her location, point a, and point c are collinear. she marks point e at this location, as shown. (a) can kayla conclude that δ and δ are similar? why or why not? (b) suppose de = 15 ft. what can kayla conclude about the width of the river?

Find the domain of the following expression: 1/(√x)-2