x^n এর সহগ নির্ণয় বিষয়ক
The coefficient of x7 x^7 x7 in the expansion of (x2+1x)11 ( x^2 + \frac {1}{x})^{11} (x2+x1)11 is
154
231
462
924
Step 1: Find value of general term for expansion\textbf{Step 1: Find value of general term for expansion}Step 1: Find value of general term for expansion
Given equation is\text{Given equation is}Given equation is
(x2+1x)11\bigg ( x^2 +\dfrac {1}{x}\bigg)^{11} (x2+x1)11
Tn=Tr+1=nCrp(n−r).qrT_n= T_{r +1 }=^nC_r p^{ (n-r)}.q^rTn=Tr+1=nCrp(n−r).qr
⇒Tn=Tr+1=11Cr.(x2)(11−r).(1x)r\Rightarrow T_n=T_{r+1} = ^{11}C_r. (x^2)^{(11-r)} .\bigg( \dfrac {1}{x}\bigg)^r ⇒Tn=Tr+1=11Cr.(x2)(11−r).(x1)r
=11Cr.(x)(22−2r).(1x)r= ^{11}C_r. (x)^{(22-2r)} .\bigg( \dfrac {1}{x}\bigg)^r =11Cr.(x)(22−2r).(x1)r
=11Cr.(x)(22−2r−r)= ^{11}C_r. (x)^{(22-2r-r)} =11Cr.(x)(22−2r−r)
=11Cr.(x)(22−3r)= ^{11}C_r. (x)^{(22-3r)} =11Cr.(x)(22−3r)
Step 2: Find value of coefficient of x7\textbf{Step 2: Find value of coefficient of x$^7$}Step 2: Find value of coefficient of x7
To obtain coefficient of x7:\text{To obtain coefficient of x}^7 : To obtain coefficient of x7:
⇒22−3r=7\Rightarrow 22-3r=7 ⇒22−3r=7
⇒\Rightarrow ⇒ 3r=153r=15 3r=15
∴\therefore ∴ r=5r=5 r=5
For r=5,6th term is given by-\text{For r=5,6th term is given by-}For r=5,6th term is given by-
T6=T5+1=11C5x(22−15)=11C5x7. T_6=T_{5+1} = ^{11}C_5 x^{(22 -15)} = ^{11}C_5 x^7 .T6=T5+1=11C5x(22−15)=11C5x7.
∴ \therefore ∴ Coefficient ofx7\text{Coefficient of} x^7 Coefficient ofx7=11C5=^{11}C_5 =11C5
=11×10×9×8×75×4×3×2×1= \dfrac { 11 \times 10 \times 9 \times 8 \times 7}{5 \times 4 \times 3 \times 2 \times 1} =5×4×3×2×111×10×9×8×7
=462 = 462 =462
Therefore,value of coefficient of x7 is 462\textbf{Therefore,value of coefficient of x$^7$ is 462}Therefore,value of coefficient of x7 is 462
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