These questions deal with factoring.  (1+z+z^2)^2 and (p^2-pq+q^2)^2 
 I partially understand the second line which would be 1+z^2+z^4+2z+2z^2+2z^3 but I don't understand where the 2 comes from in the second half of that line.  
 p.s.(^2 means squared or cubed etc.) 
 Please help me out A.S.A.P.!
 I have a quiz on this tomorrow!
 Thank-you,
 A.R.