(a) recursive equation for nodes at height h,
N(h)= nodes in LST + 1 + nodes in RST
N(h)= N(h-1) + 1 + { N(h-1) - 1 }
N(h)= 2N(h-1) ; when h>=2
by intution N(0)=1, N(1)=2
by solving above equation by back substitution (termination condition, h-k=1) we will get
N(h)= 2^{h}
(b) for h<=1
at h=1, N(1)=2
at h=0, N(0)= 1