Question 1001292
-x = sqrt(2x + 15)
square both sides of =
x^2 = 2x + 15
x^2 -2x -15 = 0
(x-5)*(x+3) = 0
x = 5 or -3
check answers
-(-3) = sqrt(9)
3 = 3
-5 = sqrt(25)
-5 = 5
*************************************************************************
-5 is the extraneous root
*************************************************************************
here is the graph of both equations, -x is red and sqrt(2x+15) is green
{{{ graph( 300, 200, -10, 2, -2, 10, -x, sqrt(2x+15)) }}} 
solution is the intersection of the equations, therefore
x = -3