The problem is to find $\frac{dy}{dx}$ given the equation $\sin x + \frac{\log(2y)}{4y} = 5$. We need to use implicit differentiation.

AnalysisCalculusImplicit DifferentiationDerivativesQuotient RuleLogarithmic Function
2025/6/11

1. Problem Description

The problem is to find dydx\frac{dy}{dx} given the equation sinx+log(2y)4y=5\sin x + \frac{\log(2y)}{4y} = 5. We need to use implicit differentiation.

2. Solution Steps

Given the equation sinx+log(2y)4y=5\sin x + \frac{\log(2y)}{4y} = 5.
First, differentiate both sides with respect to xx:
ddx(sinx)+ddx(log(2y)4y)=ddx(5)\frac{d}{dx} (\sin x) + \frac{d}{dx} \left( \frac{\log(2y)}{4y} \right) = \frac{d}{dx} (5)
We know that ddx(sinx)=cosx\frac{d}{dx}(\sin x) = \cos x and ddx(5)=0\frac{d}{dx}(5) = 0.
So, cosx+ddx(log(2y)4y)=0\cos x + \frac{d}{dx} \left( \frac{\log(2y)}{4y} \right) = 0.
Now we need to find the derivative of log(2y)4y\frac{\log(2y)}{4y} with respect to xx. We'll use the quotient rule:
ddx(uv)=vdudxudvdxv2\frac{d}{dx} \left( \frac{u}{v} \right) = \frac{v \frac{du}{dx} - u \frac{dv}{dx}}{v^2}
Let u=log(2y)u = \log(2y) and v=4yv = 4y.
Then dudx=12y2dydx=1ydydx\frac{du}{dx} = \frac{1}{2y} \cdot 2 \cdot \frac{dy}{dx} = \frac{1}{y} \frac{dy}{dx}
and dvdx=4dydx\frac{dv}{dx} = 4 \frac{dy}{dx}.
So,
ddx(log(2y)4y)=4y1ydydxlog(2y)4dydx(4y)2=4dydx4log(2y)dydx16y2=4(1log(2y))dydx16y2=(1log(2y))dydx4y2\frac{d}{dx} \left( \frac{\log(2y)}{4y} \right) = \frac{4y \cdot \frac{1}{y} \frac{dy}{dx} - \log(2y) \cdot 4 \frac{dy}{dx}}{(4y)^2} = \frac{4 \frac{dy}{dx} - 4 \log(2y) \frac{dy}{dx}}{16y^2} = \frac{4 (1 - \log(2y)) \frac{dy}{dx}}{16y^2} = \frac{(1 - \log(2y)) \frac{dy}{dx}}{4y^2}
Now, plug this back into the original differentiated equation:
cosx+(1log(2y))4y2dydx=0\cos x + \frac{(1 - \log(2y))}{4y^2} \frac{dy}{dx} = 0
Now, solve for dydx\frac{dy}{dx}:
(1log(2y))4y2dydx=cosx\frac{(1 - \log(2y))}{4y^2} \frac{dy}{dx} = -\cos x
dydx=4y2cosx1log(2y)=4y2cosxlog(2y)1\frac{dy}{dx} = \frac{-4y^2 \cos x}{1 - \log(2y)} = \frac{4y^2 \cos x}{\log(2y) - 1}
Multiply both the numerator and denominator by -1:
dydx=4y2cosx1log(2y)\frac{dy}{dx} = -\frac{4y^2 \cos x}{1 - \log(2y)}.
The given solution is:
dydx=3y2cosx4log(2y)\frac{dy}{dx} = -\frac{3 y^2 \cos x}{4 - \log(2y)}
The correct derivative of log(2y)log(2y) with respect to x is 12y2dydx=1ydydx\frac{1}{2y} * 2 * \frac{dy}{dx} = \frac{1}{y} \frac{dy}{dx}.
The correct derivative of 4y4y with respect to x is 4dydx4 \frac{dy}{dx}.
Using quotient rule on log(2y)4y\frac{log(2y)}{4y} will give:
4y1ydydxlog(2y)4dydx(4y)2=4dydx4log(2y)dydx16y2=(1log(2y))dydx4y2\frac{4y*\frac{1}{y}\frac{dy}{dx} - log(2y)*4\frac{dy}{dx}}{(4y)^2} = \frac{4\frac{dy}{dx} - 4log(2y)\frac{dy}{dx}}{16y^2} = \frac{(1-log(2y))\frac{dy}{dx}}{4y^2}.
Therefore dydx=4y2cos(x)1log(2y)\frac{dy}{dx} = - \frac{4y^2cos(x)}{1 - log(2y)}.
The question must be a copy error. The equation for dydx\frac{dy}{dx} is most probably:
dydx=4y2cosx4log(2y)\frac{dy}{dx} = -\frac{4 y^2 \cos x}{4 - \log(2y)}.
This gives:
cosx+dydx1log(2y)4y2=0cos x + \frac{dy}{dx}\frac{1 - log(2y)}{4y^2} = 0
dydx1log(2y)4y2=cosx\frac{dy}{dx}\frac{1 - log(2y)}{4y^2} = -cos x
dydx=4y2cosx1log(2y)\frac{dy}{dx} = -\frac{4y^2cos x}{1 - log(2y)}
If we wish to obtain 3y2cosx4log(2y)-\frac{3 y^2 \cos x}{4 - \log(2y)}, there is no algebraic way from the given equation.

3. Final Answer

dydx=4y2cosx1log(2y)\frac{dy}{dx} = - \frac{4y^2 \cos x}{1 - \log(2y)}. Assuming there was a typo in the question, a more likely solution would be: dydx=4y2cosx4log(2y)\frac{dy}{dx} = -\frac{4 y^2 \cos x}{4 - \log(2y)}

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