What are the solutions of the equation x^4-5x-^2-14=0

So you want to start to factor  so you get (x²+2)(x²-7) = 0.  Now set each () to 0, so you get  (x²+2) = 0 and  (x²-7)=0.  The first ends with +√2i and -√2i, the second ends with +√7 and -√7