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If 
(dy)/(dx)=ky where 
k is a constant, and 
y(0)=100, then 
y(3)
A. 
100e^(k)

(dy)/(dx)=ky rarr int(1)/(y)dy+(kdx
B. 
300e^(k)

ln(y)=kx+c
C. 
100e^(3k)

ln()=
D. 
300e^(3k)

If dydx=ky \frac{d y}{d x}=k y where k k is a constant, and y(0)=100 y(0)=100 , then y(3) y(3) \newlineA. 100ek 100 e^{k} \newlinedydx=ky1ydy+(kdx \frac{d y}{d x}=k y \rightarrow \int \frac{1}{y} d y+(k d x \newlineB. 300ek 300 e^{k} \newlineln(y)=kx+c \ln (y)=k x+c \newlineC. 100e3k 100 e^{3 k} \newlineln()= \ln ()= \newlineD. 300e3k 300 e^{3 k}

Full solution

Q. If dydx=ky \frac{d y}{d x}=k y where k k is a constant, and y(0)=100 y(0)=100 , then y(3) y(3) \newlineA. 100ek 100 e^{k} \newlinedydx=ky1ydy+(kdx \frac{d y}{d x}=k y \rightarrow \int \frac{1}{y} d y+(k d x \newlineB. 300ek 300 e^{k} \newlineln(y)=kx+c \ln (y)=k x+c \newlineC. 100e3k 100 e^{3 k} \newlineln()= \ln ()= \newlineD. 300e3k 300 e^{3 k}
  1. Separate and Integrate: Solve the differential equation dydx=ky\frac{dy}{dx} = ky. To solve this first-order linear differential equation, we separate variables and integrate both sides.
  2. Perform Integration: Separate variables and integrate.\newlineWe write the equation as (1y)dy=kdx(\frac{1}{y})dy = kdx and integrate both sides.\newline(1y)dy=kdx\int(\frac{1}{y})dy = \int kdx
  3. Solve for yy: Perform the integration.\newlineThe integral of 1y\frac{1}{y}dy is lny\ln|y|, and the integral of kdxkdx is kxkx. So we have:\newlinelny=kx+C\ln|y| = kx + C, where CC is the constant of integration.
  4. Determine Constant CC: Solve for yy.\newlineTo solve for yy, we exponentiate both sides of the equation to get rid of the natural logarithm.\newlineelny=ekx+Ce^{\ln|y|} = e^{kx + C}\newliney=ekxeC|y| = e^{kx} \cdot e^C\newlineSince yy is positive (given y(0)=100y(0) = 100), we can drop the absolute value:\newliney=ekxeCy = e^{kx} \cdot e^C
  5. Substitute for CC: Determine the constant CC using the initial condition y(0)=100y(0) = 100. Substitute x=0x = 0 and y=100y = 100 into the equation y=ekxeCy = e^{kx} \cdot e^C to find CC. 100=ek0eC100 = e^{k\cdot 0} \cdot e^C 100=e0eC100 = e^0 \cdot e^C 100=1eC100 = 1 \cdot e^C CC00
  6. Substitute CC into yy: Substitute CC back into the equation for yy.
    y=ekxeln(100)y = e^{kx} \cdot e^{\ln(100)}
    y=ekx100y = e^{kx} \cdot 100
  7. Find y(3)y(3): Find y(3)y(3).\newlineSubstitute x=3x = 3 into the equation y=ekx×100y = e^{kx} \times 100 to find y(3)y(3).\newliney(3)=ek×3×100y(3) = e^{k\times 3} \times 100\newliney(3)=100e3ky(3) = 100e^{3k}

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