please download the lecture note to understand my question. 1. What is the difference between (I) and (I bar) ? is I = I bar?they are the same? 2.in the slide i uploaded, chapter5.8 pg 31, the equation for rectangle, (I bar x prime) = (1/12bh cube) and (Ix) = (1/3bh cube) ,as you can see,their equation are different. I know (I bar x prime) = (1/12bh cube) is used in the equation (Ix)= (1/12bh cube+ Ady square) , but when to use this equation (Ix) = (1/3bh cube) ? p/s:I am an engineering student from malaysia university.