JEE Mains Model Paper 24

difference of suffices is same =10 and terms are alternately positive and negative
∴ take expansion of (1−x)30 and (x+1)30 ,
multiply and equate cofficient of x20 on both sides
(1−x)30 (x+1)30 = (1−x2)30
∴ coff pf x20 =

30

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C10