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    				| 1. | यदि x = 4, y =3, z = 2 तब सिद्ध कीजिए कि 4x2 + y2 + 25z2 + 4xy – 10yz – 20xz =1 | 
| Answer» L.H.S. = 4x2 + y2 + 25z2 + 4xy -10yz – 20xz = (-2x)2 + (-y)2 + (58)2 + 2(-2x)(-y) + 2(-y) (5z) + 2(5z)(-2x) = (-2x – y + 5z)2 = (-2 × 4 – 3 + 5 × 2)2 = (-1)2 = 1 = R.H.S. | |