JEE MAIN - Mathematics (2022 - 29th July Evening Shift - No. 8)
Let $$y=y(x)$$ be the solution curve of the differential equation $$ \frac{d y}{d x}+\left(\frac{2 x^{2}+11 x+13}{x^{3}+6 x^{2}+11 x+6}\right) y=\frac{(x+3)}{x+1}, x>-1$$, which passes through the point $$(0,1)$$. Then $$y(1)$$ is equal to :
$$\frac{1}{2}$$
$$\frac{3}{2}$$
$$\frac{5}{2}$$
$$\frac{7}{2}$$
Explanation
$\frac{d y}{d x}+\left(\frac{2 x^{2}+11 x+13}{x^{3}+6 x^{2}+11 x+6}\right) y=\frac{(x+3)}{x+1}, x>-1$,
Integrating factor I.F. $=e^{\int \frac{2 x^{2}+11 x+13}{x^{3}+6 x^{2}+11 x+6} d x}$
$$ \begin{aligned} & \text { Let } \frac{2 x^{2}+11 x+13}{(x+1)(x+2)(x+3)}=\frac{A}{x+1}+\frac{B}{x+2}+\frac{C}{x+3} \\\\ & A=2, B=1, C=-1 \\\\ & \text { I.F. }=e^{(2 \ln |x+1|+\ln |x+2|-\ln |x+3|)} \\\\ & =\frac{(x+1)^{2}(x+2)}{x+3} \end{aligned} $$
Solution of differential equation
$$ \begin{aligned} &y \cdot \frac{(x+1)^{2}(x+2)}{x+3}=\int(x+1)(x+2) d x \\\\ &y \frac{(x+1)^{2}(x+2)}{x+3}=\frac{x^{3}}{3}+\frac{3 x^{2}}{2}+2 x+c \end{aligned} $$
Curve passes through $(0,1)$
$$ \begin{gathered} 1 \times \frac{1 \times 2}{3}=0+c \Rightarrow c=\frac{2}{3} \\\\ \text { So, } y(1)=\frac{\frac{1}{3}+\frac{3}{2}+2+\frac{2}{3}}{\frac{\left(2^{2} \times 3\right)}{4}}=\frac{3}{2} \end{gathered} $$
Integrating factor I.F. $=e^{\int \frac{2 x^{2}+11 x+13}{x^{3}+6 x^{2}+11 x+6} d x}$
$$ \begin{aligned} & \text { Let } \frac{2 x^{2}+11 x+13}{(x+1)(x+2)(x+3)}=\frac{A}{x+1}+\frac{B}{x+2}+\frac{C}{x+3} \\\\ & A=2, B=1, C=-1 \\\\ & \text { I.F. }=e^{(2 \ln |x+1|+\ln |x+2|-\ln |x+3|)} \\\\ & =\frac{(x+1)^{2}(x+2)}{x+3} \end{aligned} $$
Solution of differential equation
$$ \begin{aligned} &y \cdot \frac{(x+1)^{2}(x+2)}{x+3}=\int(x+1)(x+2) d x \\\\ &y \frac{(x+1)^{2}(x+2)}{x+3}=\frac{x^{3}}{3}+\frac{3 x^{2}}{2}+2 x+c \end{aligned} $$
Curve passes through $(0,1)$
$$ \begin{gathered} 1 \times \frac{1 \times 2}{3}=0+c \Rightarrow c=\frac{2}{3} \\\\ \text { So, } y(1)=\frac{\frac{1}{3}+\frac{3}{2}+2+\frac{2}{3}}{\frac{\left(2^{2} \times 3\right)}{4}}=\frac{3}{2} \end{gathered} $$
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