Prove these using only field axioms, order axioms and the fact that 1>0 and x0=0

a. (a^-1)^-1=a

b. a>0 iff a^-1>0

c. (ab)^-1=a^(-1)b^(-1)

d. a>1 iff 0<a^-1<1

Any help would be great.. Or just a push in the general direction, I'm not sure where to start with them, I've done similar ones but I can't seem to see any relations.