সাধারণ পদ , মধ্যপদ ও সমদূরবর্তী পদ নির্ণয়

In the expansion of (1+x)43(1 + x)^{43}, the coefficients of the (2r+1)th and the (r + 2)th terms are equal, then the value of r, is

হানি নাটস

Tn+1=nCnannbnTn+1=43CnxnT2n+1=43C2nx2nTn+2=T(n+1)+1xn+1=43Cn+1 \begin{aligned} T_{n+1} & ={ }^{n} C_{n} \cdot a^{n-n} \cdot b^{n} \\ T_{n+1} & ={ }^{43} C_{n} x^{n} \\ T_{2 n+1} & =43 C_{2 n} \cdot x^{2 n} \\ T_{n+2} & =T_{(n+1)+1} \cdot x^{n+1} \\ & =43 C_{n+1} \end{aligned}

Coefficients are equal

43c2r=43cn+1 43 c_{2 r}={ }^{43} c_{n+1}

2r=r+1 or 2n+r+1=43r=1 or 3r=42r=14 \begin{aligned} 2 r= & r+1 \quad \text { or } \\ 2 n+r+1 & =43 \\ r & =1 \text { or } \begin{aligned} 3 r & =42 \\ r & =14 \end{aligned} \end{aligned}

[ncx=ncy, then x=y or x+y=n] \left[\begin{array}{c} n c_{x}={ }^{n} c_{y} \text {, then } x=y \text { or } \\ x+y=n \end{array}\right]

Option (A) is correct

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