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Find the particular solution, 
y=f(x), to the differential equation 
(dy)/(dx)=(cos x)/(y) given 
f((3pi)/(2))=-1 and then find 
f((pi)/(2)).

Find the particular solution, y=f(x) y=f(x) , to the differential equation dydx=cosxy \frac{d y}{d x}=\frac{\cos x}{y} given f(3π2)=1 f\left(\frac{3 \pi}{2}\right)=-1 and then find f(π2) f\left(\frac{\pi}{2}\right) .

Full solution

Q. Find the particular solution, y=f(x) y=f(x) , to the differential equation dydx=cosxy \frac{d y}{d x}=\frac{\cos x}{y} given f(3π2)=1 f\left(\frac{3 \pi}{2}\right)=-1 and then find f(π2) f\left(\frac{\pi}{2}\right) .
  1. Separate and Integrate: Step 11: Separate variables and integrate.\newlineWe start by separating the variables in the differential equation dydx=cosxy\frac{dy}{dx} = \frac{\cos x}{y}. Rearrange to get ydy=cosxdxy dy = \cos x dx.\newlineIntegrate both sides:\newlineydy=cosxdx\int y dy = \int \cos x dx,\newliney22=sinx+C\frac{y^2}{2} = \sin x + C,
  2. Solve for y: Step 22: Solve for y.\newlineTo find y, rearrange the equation:\newliney2=2(sinx+C)y^2 = 2(\sin x + C),\newliney=±2(sinx+C)y = \pm\sqrt{2(\sin x + C)},
  3. Find C: Step 33: Use the initial condition to find C.\newlineGiven f(3π2)=1f\left(\frac{3\pi}{2}\right) = -1, plug in x=3π2x = \frac{3\pi}{2} and y=1y = -1:\newline(1)2=2(sin(3π2)+C)(-1)^2 = 2(\sin\left(\frac{3\pi}{2}\right) + C),\newline1=2(1+C)1 = 2(-1 + C),\newline1=2+2C1 = -2 + 2C,\newline2C=32C = 3,\newlineC=32C = \frac{3}{2},
  4. Write Solution: Step 44: Write the particular solution.\newlineWith C=32C = \frac{3}{2}, the solution becomes:\newliney=±2(sinx+32)y = \pm\sqrt{2(\sin x + \frac{3}{2})},\newlineSince f(3π2)=1f\left(\frac{3\pi}{2}\right) = -1, we choose the negative branch:\newliney=2(sinx+32)y = -\sqrt{2(\sin x + \frac{3}{2})},
  5. Find f(π2)f(\frac{\pi}{2}): Step 55: Find f(π2)f\left(\frac{\pi}{2}\right).\newlinePlug in x=π2x = \frac{\pi}{2}:\newlinef(π2)=2(sin(π2)+32)f\left(\frac{\pi}{2}\right) = -\sqrt{2(\sin\left(\frac{\pi}{2}\right) + \frac{3}{2})},\newlinef(π2)=2(1+32)f\left(\frac{\pi}{2}\right) = -\sqrt{2(1 + \frac{3}{2})},\newlinef(π2)=2×2.5f\left(\frac{\pi}{2}\right) = -\sqrt{2 \times 2.5},\newlinef(π2)=5f\left(\frac{\pi}{2}\right) = -\sqrt{5},

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