If x2+1x^2 + 1x2+1 is a factor of x4+ax3+bx2+cx+dx^4 + ax^3 + bx^2 + cx + dx4+ax3+bx2+cx+d, what relationship must hold?
a=ca=ca=c and b−d=1b-d=1b−d=1
a=ca=ca=c and b−d=0b-d=0b−d=0
a+c=0a+c=0a+c=0 and b=db=db=d
a=ca=ca=c and b=db=db=d