finding coordinates

Question

Point B has coordinates (4,1). The x-coordinate of point A is negative 5. The distance between point A and point B is 15 units. What are the possible coordinates of point A?

Answer 1

A = (-5,y)    B = (4,1)

 

(Distance from A to B) = √[(-5-4)² + (y-1)²] = 15

 

                                     √[81 + y² - 2y + 1] = 15

 

                                        y² - 2y + 82 = 225

 

                                        y² - 2y -143 = 0

 

                                        (y-13)(y+11) = 0

 

                                                        y = 13 or -11