Q. If dxdy=2−y, and if y=1 when x=1, then y=(A) 2−ex−1(B) 2−e1−x(C) 2−e−x(D) 2+e−x
Write Differential Equation: Write down the given differential equation and the initial condition.We have the differential equation dxdy=2−y and the initial condition y(1)=1.
Separate Variables: Recognize that the differential equation is a first-order linear ordinary differential equation that can be solved using separation of variables.We can rearrange the equation to separate the variables y and x:2−ydy=dx
Integrate Equations: Integrate both sides of the equation with respect to their respective variables.∫2−y1dy=∫dx
Combine Constants: Perform the integration on both sides.The left side requires a substitution to integrate. Let u=2−y, then du=−dy. The integral becomes −∫(1/u)du. The right side is straightforward: ∫dx=x+C, where C is the constant of integration.−∫(1/u)du=−ln∣u∣+C1x+C=−ln∣2−y∣+C1
Solve for y: Combine the constants of integration into a single constant.Since C1 is also a constant, we can write −ln∣2−y∣+C1 as −ln∣2−y∣+C2, where C2 is a new constant that combines C and C1.x+C2=−ln∣2−y∣
Use Initial Condition: Solve for y in terms of x. To isolate y, we first exponentiate both sides to remove the natural logarithm: e(x+C2)=e−ln∣2−y∣e(x+C2)=2−y1 Now, solve for y: 2−y=e(x+C2)1y=2−e(x+C2)1
Find Constant C2: Use the initial condition to find the value of the constant C2. We know that y(1)=1, so we substitute x=1 and y=1 into the equation: 1=2−1/e1+C2 Solve for e1+C2: e1+C2=2−1e1+C2=1 Now, take the natural logarithm of both sides to solve for C2: 1+C2=ln(1)y(1)=10y(1)=11y(1)=12
Substitute C2 into y: Substitute the value of C2 back into the equation for y.y=2−e(x−1)1This matches answer choice (A) 2−e(x−1).
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