(15+√1910i)2=125+2×15×√1910i+1910i=125+25×√19√10×√21+i+1910i
Because sqrt i = (1+i)/ sqrt2
http://web2.0calc.com/questions/what-is-square-root-of-i
=125+2√38(5√10)(1+i)+1910i
=125+2√−38050i(1+i)+95+95i50i(1+i)
=125+(2√380+95)i+9550i−50
You can do the last half yourself.