问题 选择题 已知m+1m=3,则m4+1m4的值是( )A.9B.49C.47D.1 答案 ∵m+1m=3,∴(m+1m)2=32,∴m2+1m2=9-2=7,∴(m2+1m2)2=72,∴m4+1m4=49-2=47.故选C.