JEE MAIN - Mathematics (2023 - 13th April Morning Shift - No. 5)
Explanation
The given differential equation is
$$\frac{d y}{d x} = y + 7$$
This is a first order linear differential equation and can be solved using an integrating factor.
Rearrange the equation to the standard form of a linear differential equation :
$$\frac{d y}{d x} - y = 7$$
The integrating factor is $e^{-\int dx} = e^{-x}$.
Multiplying each side of the equation by the integrating factor gives :
$$e^{-x} \frac{d y}{d x} - e^{-x} y = 7e^{-x}$$
The left-hand side of the equation is the derivative of $(e^{-x}y)$ with respect to $x$. So we can write the equation as :
$$\frac{d}{d x}(e^{-x}y) = 7e^{-x}$$
Integrate both sides with respect to $x$ :
$$e^{-x}y = -7e^{-x} + C$$
Multiply both sides by $e^{x}$ to isolate $y$ :
$$y = -7 + Ce^{x}$$
So, the general solution to the differential equation is $y = -7 + Ce^{x}$.
Now, let's apply the initial conditions to find the particular solutions :
For $y_{1}(0)=0$, we substitute into the general solution and solve for $C$ :
$$0 = -7 + C$$
So, $C = 7$, and the solution for $y_{1}$ is $y_{1}(x) = 7e^{x} - 7$.
For $y_{2}(0)=1$, again substitute into the general solution:
$$1 = -7 + C$$
So, $C = 8$, and the solution for $y_{2}$ is $y_{2}(x) = 8e^{x} - 7$.
The two curves intersect when $y_{1}(x) = y_{2}(x)$. Setting these equal and solving for $x$ gives :
$$7e^{x} - 7 = 8e^{x} - 7$$
$$e^{x} = 0$$
But $e^{x} = 0$ has no solution, because the exponential function never equals zero.
So, the curves $y=y_{1}(x)$ and $y=y_{2}(x)$ do not intersect at any point.
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