For $m, n > 0$, let $\alpha(m, n)=\int_\limits{0}^{2} t^{m}(1+3 t)^{n} d t$. If $11 \alpha(10,6)+18 \alpha(11,5)=p(14)^{6}$, then $p$ is equal to ___________.
Answer (integer)
32
Solution
We have, $\alpha(m, n)=\int\limits_0^2 t^m(1+3 t)^n d t$
<br/><br/>Also, $11 \alpha(10,6)+18 \alpha(11,5)=P(14)^6$
<br/><br/>$\Rightarrow 11 \int\limits_0^2 t^{10}(1+3 t)^6 d t+18 \int\limits_0^2 t^{11}(1+3 t)^5 d t=P(14)^6$
<br/><br/>Using integration by part for expression $t^{10}(1+3 t)^6$
<br/><br/>$$
\begin{array}{r}
\left.\Rightarrow 11\left[(1+3 t)^6 \times \frac{t^{11}}{11}\right]_0^2-\int\limits_0^2 6(1+3 t)^5 \times 3 \times \frac{t^{11}}{11} d t\right] \\\\
+18 \int\limits_0^2 t^{11}(1+3 t)^5 d t=P(14)^6
\end{array}
$$
<br/><br/>$$
\begin{aligned}
& \Rightarrow 7^6 \times 2^{11}-18 \int\limits_0^2 t^{11}(1+3 t)^5 d t+18 \int\limits_0^2 t^{11}(1+3 t)^5 d t=P(14)^6 \\\\
& \Rightarrow 7^6 \times 2^{11}=P(14)^6 \Rightarrow(7 \times 2)^6 \times 2^5=P(14)^6 \\\\
& \Rightarrow P=2^5=32
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Definite Integration · Topic: Properties of Definite Integrals
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