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, which relationship must hold between the coefficients?
a=ca=ca=c and b=d+1b=d+1b=d+1
a=ca=ca=c and d=b−1d=b-1d=b−1
a+c=b+da+c=b+da+c=b+d
a=ca=ca=c and b=1+db=1+db=1+d