$${{\mathtt{X}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{8}}{\mathtt{\,\times\,}}{\mathtt{X}}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}} = -{\mathtt{1}}$$
x2 + 8x + 15 = -1
Get all the terms to one side (add 1 to both sides):
x2 + 8x + 16 = 0
To factor: find two numbers that: when added together give you 8 and when multiplied give you 16.
(x + 4)(x + 4) = 0
When does x + 4 = 0?
When x = -4!
+1904 
