If and are positive reals satisfying , then find the maximum value of .
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I'll certainly generalise this :-).
Let a + b + c + d = M and we have to find maximum value of K = a p b q c r d s .
Writing a = p a + p a ⋯ p times , b = q b + q b ⋯ q times , c = r c + r c ⋯ r times , d = s d + s d ⋯ s times and applying AM-GM. ( p p q q r r s s K ) p + q + r + s 1 ≤ p + q + r + s M ⇒ K ≤ ( p + q + r + s M ) p + q + r + s × p p q q r r s s For equality p a = q b = r c = s d = p + q + r + s M .
In this question p = 1 , q = 2 , r = 3 , s = 4 and M = 2 0 . Substituting values we get : K ≤ 2 2 0 × 3 3 (In this question, for equality a = 2 b = 3 c = 4 d = 2 )