1.

Ifthecoefficient of(2r + 1 )thterm and(r + 2 )thterm inthe expansionof(1 + x ) ^(43 )areequal, then r is equalto

Answer»

12
14
16
18

Solution :Intheexpansion` (1 +x ) ^( 43) `
Co -efficientof` T _ (2r + 1 ) `=co- efficient of` T _ (r + 2 ) `
` RARR ""^(43)C_(2r)=""^(43)C_( r +1 ) `
`rArr2r=r + 1or2r+r+ 1=43 [because""^nC_r =""^nC_( N -r ) ] `
` rArrr= 1or 3R+ 1=43 `
` 3r=42`
`r =14 `
`thereforer= 1orr=14`


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