Q.
Coefficient of x11 in the expansion of 1+x241+x371+x412 is
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a
1051
b
1106
c
1113
d
1120
answer is C.
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Detailed Solution
2x1+3x2+4x3=11Possibilities are (0,1,2);(1,3,0);(2,1,1);(4,1,0)∴ Required coefficients = 4C0×7C1×12C2+ 4C1×7C3×12C0+ 4C2×7C1×12C1+ 4C4×7C1×1 =(1×7×66)+(4×35×1)+(6×7×12)+(1×7)=462+140+504+7=1113
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