Find all the values of a for which the equations
x^2 + ax + 1 = 0
x^2 - x - a = 2
have a common real root. Enter all the possible values, separated by commas.
x_1 + x_2 = -a
x_1 x_2 = 1
x_1 + x_2 = -1
x_1 x_2 = -a
-a=-1
1=-a
a=-1, 1
+874 
