In the last lecture we studied, when some sound is coming into this obstacle in normal direction. For example, when I whistle one kilohertz sound again [NOISE] then as you studied, this wall or partition will vibrate like this. And some wave will be reflected and some wave will be transmitted due to the vibration of this wall. But what if we have some sound coming to this flat surface of this continuity but not normal direction but having some oblique instance. For example, when I whistle like this, [NOISE] then obviously the sound were propagating to this direction therefore, the transmission would be different compared with what we have studied already. But, thinking about this kind of oblique instance then we can decompose this oblique instance will be decompose into normal instance as and the other one is very congenital this flat surface of this continuity, okay? So in this lecture we will study how this obliqueness will affect the transmission of flat surface of this continuity. Second topic is rather complicated compared with what we studied. That is the case, if this partition vibrates like this, like a plate, and we have sound instant to this plate, like this, [NOISE] then how this, the property of a plate, really affect the transmission. That is what we are going to study in this lecture.