Find the sum of all the rational terms in the expansion of
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After expansion the general term is,
C o n s t a n t × ( 2 2 1 ) x × ( 3 3 1 ) y × ( 5 6 1 ) z
Where , x + y + z = 1 0 … … … … ( 1 )
A term becomes rational iff x ∈ { 0 , 2 , 4 , 6 , 8 , 1 0 } ; y ∈ { 0 , 3 , 6 , 9 } ; z ∈ { 0 , 6 }
It can be easily found that only ( 1 0 , 0 , 0 ) , ( 4 , 6 , 0 ) , ( 4 , 0 , 6 ) these three triples make ( 1 ) true.
So there are three rational term in the expansion of ( 2 2 1 + 3 3 1 + 5 6 1 ) 1 0
And they are
( 1 0 1 0 ) ( 2 2 1 ) 1 0 × ( 3 3 1 ) 0 × ( 5 6 1 ) 0 = 3 2
( 4 1 0 ) ( 2 2 1 ) 4 × ( 3 3 1 ) 6 × ( 5 6 1 ) 0 = 7 5 6 0
( 4 1 0 ) ( 2 2 1 ) 4 × ( 3 3 1 ) 0 × ( 5 6 1 ) 6 = 4 2 0 0
So the answer is 3 2 + 7 5 6 0 + 4 2 0 0 = 1 1 7 9 2