Question 578830
{{{(2+5i)/ (1-i)}}} multiply numerator and denominator by {{{(1+i)}}}
{{{(2+5i)(1+i)/ (1-i)(1+i)=(2+5i+2i+5i^2)/(1^2-i^2)=(2+7i-5)/(1+1)=(-3+7i)/2=-3/2+(7/2)i=-1.5+3.5i}}} 
Use {{{i^2=-1}}}