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If (dy)/(dx)=2-y, and if y=1 when x=1, then y=
(A) 2-e^(x-1)
(B) 2-e^(1-x)
(C) 2-e^(-x)
(D) 2+e^(-x)

If dydx=2y \frac{d y}{d x}=2-y , and if y=1 y=1 when x=1 x=1 , then y= y= \newline(A) 2ex1 2-e^{x-1} \newline(B) 2e1x 2-e^{1-x} \newline(C) 2ex 2-e^{-x} \newline(D) 2+ex 2+e^{-x}

Full solution

Q. If dydx=2y \frac{d y}{d x}=2-y , and if y=1 y=1 when x=1 x=1 , then y= y= \newline(A) 2ex1 2-e^{x-1} \newline(B) 2e1x 2-e^{1-x} \newline(C) 2ex 2-e^{-x} \newline(D) 2+ex 2+e^{-x}
  1. Write Differential Equation: Write down the given differential equation and the initial condition.\newlineWe have the differential equation dydx=2y\frac{dy}{dx} = 2 - y and the initial condition y(1)=1y(1) = 1.
  2. Separate Variables: Recognize that the differential equation is a first-order linear ordinary differential equation that can be solved using separation of variables.\newlineWe can rearrange the equation to separate the variables yy and xx:\newlinedy2y=dx\frac{dy}{2 - y} = dx
  3. Integrate Equations: Integrate both sides of the equation with respect to their respective variables.\newline12ydy=dx\int\frac{1}{2 - y}\, dy = \int dx
  4. Combine Constants: Perform the integration on both sides.\newlineThe left side requires a substitution to integrate. Let u=2yu = 2 - y, then du=dydu = -dy. The integral becomes (1/u)du-\int(1/u) \, du. The right side is straightforward: dx=x+C\int dx = x + C, where CC is the constant of integration.\newline(1/u)du=lnu+C1-\int(1/u) \, du = -\ln|u| + C_1\newlinex+C=ln2y+C1x + C = -\ln|2 - y| + C_1
  5. Solve for yy: Combine the constants of integration into a single constant.\newlineSince C1C_1 is also a constant, we can write ln2y+C1-\ln|2 - y| + C_1 as ln2y+C2-\ln|2 - y| + C_2, where C2C_2 is a new constant that combines CC and C1C_1.\newlinex+C2=ln2yx + C_2 = -\ln|2 - y|
  6. Use Initial Condition: Solve for yy in terms of xx. To isolate yy, we first exponentiate both sides to remove the natural logarithm: e(x+C2)=eln2ye^{(x + C_2)} = e^{-\ln|2 - y|} e(x+C2)=12ye^{(x + C_2)} = \frac{1}{2 - y} Now, solve for yy: 2y=1e(x+C2)2 - y = \frac{1}{e^{(x + C_2)}} y=21e(x+C2)y = 2 - \frac{1}{e^{(x + C_2)}}
  7. Find Constant C22: Use the initial condition to find the value of the constant C2C2. We know that y(1)=1y(1) = 1, so we substitute x=1x = 1 and y=1y = 1 into the equation: 1=21/e1+C21 = 2 - 1/e^{1 + C2} Solve for e1+C2e^{1 + C2}: e1+C2=21e^{1 + C2} = 2 - 1 e1+C2=1e^{1 + C2} = 1 Now, take the natural logarithm of both sides to solve for C2C2: 1+C2=ln(1)1 + C2 = \ln(1) y(1)=1y(1) = 100 y(1)=1y(1) = 111 y(1)=1y(1) = 122
  8. Substitute C2C_2 into yy: Substitute the value of C2C_2 back into the equation for yy.\newliney=21e(x1)y = 2 - \frac{1}{e^{(x - 1)}}\newlineThis matches answer choice (A) 2e(x1)2 - e^{(x - 1)}.

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