问题 选择题 若a2=25,b=9,则a+b=( )A.8B.±8C.8或-2D.2或-8 答案 ∵a2=25,b=9,∴a=±5,b=3,当a=5,b=3,a+b=5+3=8;当a=-5,b=3,a+b=-5+3=-2.故选C.