I was referring to this wiki article related to forward and backward algorithm
Actually, I didn't get this part $ \frac{P(o_1,o_2..o_T,X_t=x_i|\pi)}{P(o_1,o_2..o_T|\pi)} = \frac{f_{0:t}(i)*b_{t:T}(i)}{\prod_{s=1}^{T}c_s} $
where f denotes the forward algorithm and b denotes the backward algorithm. I didn't get how the probability became the factor of the two. I couldn't derive it. I tried to use chain rule of probability but somehow couldn't derive it. Any suggestions?