sqrt(-24)
You'd have your answer much faster if you'd googled this problem.
http://www.google.com/#hl=en&sugexp=cqn&gs_nf=1&pq=9.8%20%2B%207.39%20%3D%20&cp=9&gs_id=o&xhr=t&q=sqrt(-24)&pf=p&sclient=psy-ab&oq=sqrt(-24)&aq=&aqi=&aql=&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=3c17bac594aba933&biw=711&bih=453&bs=1