(1)∵z为实数,∴虚部a 2-5a-6=0,解得a=6或-1.
(2)∵z为虚数,∴虚部a 2-5a-6≠0,解得a≠6,且a≠-1.
(3)∵z为纯虚数,∴
a 2 -7a+6=0
a 2 -5a-6≠0 ,解得a=1.
综上可知:(1)当a=-1或6时,z为实数;
(2)当a≠6,且a≠-1时,z为虚数;
(3)当a=1时,z为纯虚数.
(1)∵z为实数,∴虚部a 2-5a-6=0,解得a=6或-1.
(2)∵z为虚数,∴虚部a 2-5a-6≠0,解得a≠6,且a≠-1.
(3)∵z为纯虚数,∴
a 2 -7a+6=0
a 2 -5a-6≠0 ,解得a=1.
综上可知:(1)当a=-1或6时,z为实数;
(2)当a≠6,且a≠-1时,z为虚数;
(3)当a=1时,z为纯虚数.