 In this problem, we are going to take up a question related to a special identity which we learned in the previous session and the question is, find the product of these two factors, what all? xy, x-y plus 2z, nx square plus y square plus 4z square, plus xy plus 2yz minus 2zx, okay. Now, the moment we see such kind of problems and you see how do we approach? Basically, the thing is, what should be the idea as in, what should be the first step? So, if you see, this is a trinomial, isn't it? So, if you see, there are trinomials involved, trinomials involved. And in case of trinomials, we know, we studied trigonometry, sorry, identity is related to trinomial square, trinomial square, if you remember, a plus b plus c whole square, that was one thing which we learned. And then we also talked, we had a special identity where we had trinomial and this kind of an expression. So, that special identity was nothing but a plus b plus c times a square plus b square plus c square minus a v minus b c minus c a. And this identity was given as a cube plus b cube plus c cube minus 3abc, isn't it? This is what we learned in the previous session. So, the way this has been organized, these two factors have been given, it indicates that obviously, first is there is trinomial and there are square terms in the second factor, if you see, x square, y square, z square. So, it is inviting us to think in these lines. Okay. So, hence, and you can rule out that it is not a square identity, not related to square. Why? Because if you multiply, you will get a cube, x into x square will you will get a cube. So, hence, it is something related to cube as well as trinomials and the only identity which we have learned is this one. Let us see whether this fits into the scheme. So, clearly, I can rewrite the given expression as x minus y or you can rather say it as x plus minus y plus 2z, right? So, this becomes my 3 a and b and c. So, you can think x as a, this minus y is b and 2z as c. Then the second term, the other term will be nothing but a square, then plus minus y whole square because minus y whole square or plus y square are same thing. And 2z, 2z whole square, then in plus plus x times, then you can rather write this as x minus x times minus y, then minus minus y times 2z and minus 2z times x. So, this is the second factor, right? These are the terms which I can write the given expression into. So, if you see, this clearly indicates this is a, this is b, this is c and these ones are a square, b square, c square, minus a, b, minus b, c and minus c, a, right? Which fits into this identity. Hence, the final result would be nothing but x cube plus minus y whole cube because minus y is playing the role of b and 2z whole cube, then minus 3 times a, sorry, so a is, a here is, what? a is, a is x, b is minus y and c is 2z. So hence, answer would be x cube and then minus y whole cube is nothing but minus y cube plus a z cube and then this is nothing but minus and minus becomes plus, so 6xyz, why 6? 3 into 2 is 6xyz. So, this should be the answer or this should be the final product when you multiply these things, right? x cube plus y cube plus a z cube plus 6xyz.