Question

Point B has coordinates (−4, −2). The x-coordinate of point A is 5. The distance between points A and B is 15 units. What are the possible coordinates of point A?

Answer 1

$~~~~~~~~~~~~\textit{distance between 2 points} \\\\ A(\stackrel{x_1}{5}~,~\stackrel{y_1}{y})\qquad B(\stackrel{x_2}{-4}~,~\stackrel{y_2}{-2})\qquad \qquad d = \sqrt{( x_2- x_1)^2 + ( y_2- y_1)^2} \\\\\\ \stackrel{AB}{15}=\sqrt{[-4 - 5]^2 + [-2 - y]^2}\implies 15^2=(-9)^2+(-2-y)^2$

$225=81+(-2-y)(-2-y)\implies 225=81+\stackrel{F~O~I~L}{(4+4y+y^2)} \\\\\\ 144=4+4y+y^2\implies 0=y^2+4y-140\implies 0=(y-10)(y+14) \\\\\\ y= \begin{cases} 10\\ -14 \end{cases}\qquad \qquad \qquad A(5~~,~~10)\qquad A(5~~,~~-14)$