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QJEEM24Maaf0a: JEE Main 2024 Mathematics - Class 11 JEEM24Maaf0a Solution: If the second, third and fourth terms in the expansion of are…

If the second, third and fourth terms in the expansion of (x+y)n(x+y)^n are 135, 30 and 103\frac{10}{3} , respectively, then 6(n3+x2+y)6\left(n^3+x^2+y\right) is equal to __________.

Step-by-Step Verified Solution

amp;T2=nC1y1⋅xn−1=135amp;T3=nC2y2⋅xn−2=30amp;T4=nC3y3xn−3=103\begin{aligned}& T_2={ }^n C_1 y^1 \cdot x^{n-1}=135 \\& T_3={ }^n C_2 y^2 \cdot x^{n-2}=30 \\& T_4={ }^n C_3 y^3 x^{n-3}=\frac{10}{3}\end{aligned}

⇒13530amp;=(xy)n⋅2n(n−1)=(2n−1)(xy)... (i)30103amp;=n(n−1)23!n(n−1)(n−2)(xy)9amp;=(3n−2)(xy)\begin{aligned}\Rightarrow \frac{135}{30} & =\left(\frac{x}{y}\right) \frac{n \cdot 2}{n(n-1)}=\left(\frac{2}{n-1}\right)\left(\frac{x}{y}\right) \quad \text{... (i)}\\\frac{30}{\frac{10}{3}} & =\frac{n(n-1)}{2} \frac{3!}{n(n-1)(n-2)}\left(\frac{x}{y}\right) \\9 & =\left(\frac{3}{n-2}\right)\left(\frac{x}{y}\right)\end{aligned}

⇒amp;3(n−2)=13560(n−1)⇒n=5⇒amp;x=9y.... (i)amp;y⋅x4=27⇒x9⋅x4=33⇒amp;x5=35⇒x=3y=13⇒amp;6(53+32+13)=6(125+9+13)\begin{aligned}\Rightarrow & 3(n-2)=\frac{135}{60}(n-1) \Rightarrow n=5 \\\Rightarrow & x=9 y \quad \text{.... (i)}\\& y \cdot x^4=27 \Rightarrow \frac{x}{9} \cdot x^4=3^3 \\\Rightarrow & x^5=3^5 \Rightarrow x=3 y=\frac{1}{3} \\\Rightarrow & 6\left(5^3+3^2+\frac{1}{3}\right)=6\left(125+9+\frac{1}{3}\right)\end{aligned}

=6(134)+2=806=6(134)+2=806

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