a)

1.Sg2?

1...Kd4 2.Qb5 Ke4 3.Rh4#

but: 1...Kc5!

1.Sg6?, Kc5!; 1.Rc3?, Ke5!; 1.Kd3?, Kc5!

1.Ra3! ~ 2.Ra5+

2...Ke4 3.Qc4#

2...Kd4 3.Qd3#

1...Ke4 2.Qa5 ~ 3.Ra4#

2...Kf4 3.Qf5#

1...Kd4 2.Qb5 Ke4 3.Ra4#

1...Kc5 2.Kd3

2...Kb4 3.Qa5#

2...Kd5 3.Ra5#

1...Ke5 2.Ke3 ~ 3.Ra5#

b) 

1.Qb6?, Kc4!; 1.Sg6?, Kc5!

1.Sf5!

1...Ke4/Ke5 2.Re3+

2...Kxf5/Kf4 3.Qf1#

2...Kd5 3.Qb5#

1...Kc5 2.Rh4 Kd5 3.Qd6#