Hi Sam,

Add $-y$ to each side of the equation to get $x^2 + x + c - y = 0.$ You can now use the General Quadratic expression to write $x$ as an expression involving $y.$ This is the inverse of your function $y = x^2 + x + c.$ There is a $\pm$ in this expression and hence the inverse can be written as two expressions, one with the $+$ sign and the other with the $-$ sign.

I hope this helps,
Penny