Let $a$ and $b$ be real numbers such that the quadratic equations $x^2 + ax + b = 0$ and $ax^2 + bx + 1 = 0$ have a root in common. Enter all possible values of $a + b,$ separated by commas.
Not totally sure about this one.....but.....here's what I found
Using the second equation
ax^2 + bx + 1 = 0
ax^2 + bx = -1
x ( ax + b) = -1
ax + b = -1/x
Sub this into the first equation
x^2 - 1/x = 0 multiply through by x
x^3 - 1 = 0 factor as a difference of cubes
( x - 1) (x^2 + x + 1) = 0
Only the first produces a single real solution x = 1
So....using the first equation
(1)^2 + a(1) + b = 0
1 + a + b = 0
a + b = -1