I have figured out the answer to the question, but I have no idea why and how it works. I have attached a copy of the question. I do apologize I am still having trouble putting in to latex, I can install some but not all, so bare with me. So if I multiple out the matrices I get [itex]\chi[/itex]2 + 10[itex]\rightarrow[/itex] I then minus this from the quadratic [itex]\chi[/itex]2 + 8[itex]\chi[/itex] + 10 = 0 [itex]\rightarrow[/itex] Which then gives me 8[itex]\chi[/itex] = 0 reagrange and I have [itex]\chi[/itex] = -8 Which is the right answer, I checked the mark scheme but I am suppose to find the value of K and not x. This make me think I have done the wrong maths but got the right answer. Could someone point out if I have gone wrong, it would be very helpful. It is the one highlighted.