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(dy)/(dx)=-4y, and 
y=3 when 
x=2.
Solve the equation.
Choose 1 answer:
(A) 
y=3e^(-4x)
(B) 
y=6e^(-4x)
(C) 
y=3e^(8-4x)
(D) 
y=3e^(4-4x)

dydx=4y \frac{d y}{d x}=-4 y , and y=3 y=3 when x=2 x=2 .\newlineSolve the equation.\newlineChoose 11 answer:\newline(A) y=3e4x y=3 e^{-4 x} \newline(B) y=6e4x y=6 e^{-4 x} \newline(C) y=3e84x y=3 e^{8-4 x} \newline(D) y=3e44x y=3 e^{4-4 x}

Full solution

Q. dydx=4y \frac{d y}{d x}=-4 y , and y=3 y=3 when x=2 x=2 .\newlineSolve the equation.\newlineChoose 11 answer:\newline(A) y=3e4x y=3 e^{-4 x} \newline(B) y=6e4x y=6 e^{-4 x} \newline(C) y=3e84x y=3 e^{8-4 x} \newline(D) y=3e44x y=3 e^{4-4 x}
  1. Recognize Type of Differential Equation: Recognize the type of differential equation. The given differential equation dydx=4y\frac{dy}{dx} = -4y is a first-order linear homogeneous differential equation with a constant coefficient.
  2. Solve the Equation: Solve the differential equation.\newlineTo solve this equation, we can use separation of variables. We rearrange the terms to get dyy=4dx\frac{dy}{y} = -4 dx and then integrate both sides.\newline1ydy=4dx\int \frac{1}{y} dy = \int -4 dx
  3. Perform the Integration: Perform the integration.\newlineThe integral of 1y\frac{1}{y} with respect to yy is lny\ln|y|, and the integral of 4-4 with respect to xx is 4x-4x. So we have:\newlinelny=4x+C\ln|y| = -4x + C, where CC is the constant of integration.
  4. Solve for y: Solve for y.\newlineTo solve for y, we exponentiate both sides to get rid of the natural logarithm:\newlineelny=e4x+Ce^{\ln|y|} = e^{-4x + C}\newliney=e4xeCy = e^{-4x} \cdot e^C\newlineSince eCe^C is just a constant, we can rename it as CC':\newliney=Ce4xy = C'e^{-4x}
  5. Apply Initial Condition: Apply the initial condition to find CC'. We are given that y=3y = 3 when x=2x = 2. We substitute these values into the equation to find CC': 3=Ce(42)3 = C'e^{(-4\cdot2)} 3=Ce(8)3 = C'e^{(-8)} C=3e8C' = \frac{3}{e^{-8}}
  6. Calculate CC': Calculate the value of CC'.\newlineTo find CC', we calculate 3e8\frac{3}{e^{-8}}:\newlineC=3×e8C' = 3 \times e^8\newlineThis is incorrect because we should have divided by e8e^{-8}, not multiplied. This is a math error.

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