答:
lim (an^2+bn)/(n+1) = 2,
所以a=0,否则当n趋向无穷大时,该式也趋向无穷大.
lim bn/(n+1) = 2,
lim [b-b/(n+1) = 2,
b=2.
所以a+b=0+2=2.