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QJEEM23Ma762f: JEE Main 2023 Mathematics - Class 12 JEEM23Ma762f Solution: Let y = y 1 ( x ) and y = y 2 ( x ) be the solution curves of…

Let y=y1(x) and y=y2(x) be the solution curves of the differential equation dydx=y+7 with initial conditions y1(0)=0 and y2(0)=1 respectively. Then the curves y=y1(x) and y=y2(x) intersect at

Multiple Choice Options

  • A no point
  • B two points
  • C infinite number of points
  • D one point

Step-by-Step Verified Solution

The given differential equation is

dydx=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 :

dydx−y=7

The integrating factor is e−∫dx=e−xe^{-\int dx} = e^{-x} .

Multiplying each side of the equation by the integrating factor gives :

e−xdydx−e−xy=7e−x

The left-hand side of the equation is the derivative of (e−xy)(e^{-x}y) with respect to xx . So we can write the equation as :

ddx(e−xy)=7e−x

Integrate both sides with respect to xx :

e−xy=−7e−x+C

Multiply both sides by exe^{x} to isolate yy :

y=−7+Cex

So, the general solution to the differential equation is y=−7+Cexy = -7 + Ce^{x} .

Now, let's apply the initial conditions to find the particular solutions :

For y1(0)=0y_{1}(0)=0 , we substitute into the general solution and solve for CC :

0=−7+C

So, C=7C = 7 , and the solution for y1y_{1} is y1(x)=7ex−7y_{1}(x) = 7e^{x} - 7 .

For y2(0)=1y_{2}(0)=1 , again substitute into the general solution:

1=−7+C

So, C=8C = 8 , and the solution for y2y_{2} is y2(x)=8ex−7y_{2}(x) = 8e^{x} - 7 .

The two curves intersect when y1(x)=y2(x)y_{1}(x) = y_{2}(x) . Setting these equal and solving for xx gives :

7ex−7=8ex−7

ex=0

But ex=0e^{x} = 0 has no solution, because the exponential function never equals zero.

So, the curves y=y1(x)y=y_{1}(x) and y=y2(x)y=y_{2}(x) do not intersect at any point.

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