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Let f be a function such that f (mn) = f (m) f (n) for every positive integers m and n. If f (1), f (2) and f (3) are positive integers, f (1) < f (2), and f (24) = 54, then f (18) equals (type in box) |
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Answer» Calculation: Let the value of f(2) and f(3) be ‘x’ and ‘y’ respectively, ⇒ f(24) = f(8).f(3) = f(2).f(2).f(2).f(3) = 54 ⇒ x3y = 54 ⇒ x3y = 27 × 2 ⇒ x3y = 33 × 2 On comparing, x = 3 and y = 2 ⇒ f(2) = 3 ⇒ f(3) = 2 ⇒ f(18) = f(9).f(2) = f(3).f(3).f(2) ⇒ f(18) = 2 × 2 × 3 ⇒ f(18) = 12 ∴ The value of f(18) equals 12. |
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