(1)当n=1时,a2=√[(6+a1)/2]=√[(6+4)/2]=√5<√16=4所以a2<a1,成立假设n=k时,ak>ak+1ak+1=√[(6+ak)/2]则当n=k+1时,ak+2=√[(6+ak+1)/2]因为ak+1<ak所以√[(6+ak+1)/2]<√[(6+ak)/2]即ak+2<√[(6+ak)/2]又因为ak+1=√[(6+ak)/2]所以ak+2<ak+1综上,命题成立。