JEE Advanced 2021Paper 2
- Exam
- JEE Advanced
- Year
- 2021
- Paper
- Paper 2
- Subject
- Mathematics
- Chapter
- Differential Equations
JEE Advanced 2021 · Paper 2 · Mathematics · Differential Equations
For any real numbers α and β , let y _ α, β (x), x ∈ R , be the...
For any real numbers and , let , be the solution of the differential equation
Let . Then which of the following functions belong(s) to the set ?
Options
- A
- B
- C
- D
Correct answer
A.
Step-by-step solution
(\frac{d y}{d x}+a y=x e^{\beta x})
Integrating factor (I.F.) (=\mathrm{e}^{\mathrm{adx}}=\mathrm{e}^{\mathrm{ax}})
So, the solution is (y \cdot e^{a x}=\int x e^{\beta x} \cdot e^{a x} d x)
(\Rightarrow y e^{a x}=\int x e^{(\alpha+\beta) x} d x)
If (\alpha+\beta \neq 0)
(\Rightarrow y e^{a x}=x \frac{e^{(\alpha+\beta) x}}{(\alpha+\beta)}-\frac{e^{(\alpha+\beta) x}}{(\alpha+\beta)^2}+C)
(\Rightarrow y=\frac{x e^{\beta x}}{(\alpha+\beta)}-\frac{e^{\beta x}}{(\alpha+\beta)^2}+C e^{-a x})
(\Rightarrow y=\frac{e^{\beta x}}{(\alpha+\beta)}\left(x-\frac{1}{a+\beta}\right)+C e^{-\alpha x})
Put (\alpha=\beta=1) in (1)
(y=\frac{e^x}{2}\left(x-\frac{1}{2}\right)+C e^{-x})
(1=\frac{e}{2} \times \frac{1}{2}+\frac{C}{e} \Rightarrow c=e-\frac{e^2}{4})
So, (y=\frac{e^x}{2}\left(x-\frac{1}{2}\right)+\left(e-\frac{e^2}{4}\right) e^{-x})
If (\alpha+\beta=0 \& \alpha=1)
)
Solution is (y e^x=\int x d x)
(\Rightarrow y e^x=\frac{x^2}{2}+C)
(y=\frac{x^2}{2} e^{-x}+C e^{-x})
(1=\frac{1}{2 e}+\frac{C}{e} \Rightarrow C=e-\frac{1}{2})
(y=\frac{x^2}{2} e^{-x}+\left(e-\frac{1}{2}\right) e^{-x})$