# TeaScript, 22 bytes <s>30 31</s>

    [d=y/2+$s(y*y/4-x),y-d
Not *that* bad. Would be much shorter if I could of gotten some golfing features finished earlier such as unicorn shortcuts 

[Try it online][1]

 [1]: http://vihanserver.tk/p/TeaScript/#?code=%22%5B(y%2B(d%3D$s(y*y-4*x)))%2F2,(y-d)%2F2%5D%22&inputs=%5B%22-63%22,%222%22%5D&opts=%7B%22int%22:true,%22ar%22:false,%22debug%22:false%7D