well, the thing about graphing is that once you have your answers, you can then start to work backwards sometimes, and then you'll realize how to do it. that's how I did a lot of trig homework xD
Anyways, -2.61etc *2 +3 +sqrt5 happens to be 0 so I'm pleased that that answer was correct
-.381etc * 2 +3 -sqrt5 is also zero 8)
sorry i can't help you do it algebraicly