Practicing Success
If a2 + b2 + c2 + 216 = 12(a + b - 2c) then \(\sqrt {ab-bc-ca}\) is equal to: |
6\(\sqrt {5}\) 4\(\sqrt {5}\) 3\(\sqrt {5}\) 8\(\sqrt {5}\) |
6\(\sqrt {5}\) |
⇒ a2 + b2 + c2 + 216 = 12(a + b - 2c) ⇒ a2 + b2 + c2 + 216 = 2(6a + 6b - 12c) ⇒ a2 + b2 + c2 - 2(6a) - 2(6b) + 2(12c) + (36 + 36 + 144) = 0 ⇒ [a2 + 36 - 2(6a)] + [b2 + 36 - 2(6b)] + [c2 + 144 + 2(12c) ] = 0 ⇒ (a - 6)2 + (b - 6)2 + (c + 12)2 = 0 from this we can directly conclude that a = 6, b = 6 and c = -12 Now, ⇒ \(\sqrt {ab - bc - ca}\) = \(\sqrt {(6×6) + (12×6) + (12×6)}\) =\(\sqrt {180}\) = 6\(\sqrt {5}\) |