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    				| 1. | सिद्ध कीजिए कि (x + y + z)2 – (x – y – z)2 = 4x ( y + z) | 
| Answer» L.H.S. = (x + y + z)2 – (x – y – z)2 = x2 + y2 + z2 + 2(xy + yz + zx) – (x2 + y2 + z2 – 2xy + 2yz – 2zx) = 4xy + 4xz = 4x(y + z) = R.H.S. | |