$x^4+ax^3+bx^2+cx+d = 0$

If the **sum** of the first two roots of the equation is equal to the **sum** of the last two roots, then find the range of values of $\displaystyle c$, such that, $\displaystyle b+c = 1$ and $a\neq -2$

**Details and Assumptions:**

$\bullet$ The roots may also be complex.

$\bullet$ $a,b,c,d$ are real numbers.