The parametric equations of a curve are
\(x = 2t - an t\), \(y = \\ln(\\\sin 2t)\),
for \(0 < t < \\frac{1}{2}\\pi\).
Show that \(\\frac{dy}{dx} = \\cot t\).
Solution
First, find \(\\frac{dx}{dt}\):
\(\\frac{dx}{dt} = \\frac{d}{dt}(2t - \\tan t) = 2 - \\sec^2 t\).
Next, find \(\\frac{dy}{dt}\):
\(\\frac{dy}{dt} = \\frac{d}{dt}(\\ln(\\sin 2t)) = \\frac{1}{\\sin 2t} \\cdot \\frac{d}{dt}(\\sin 2t) = \\frac{1}{\\sin 2t} \\cdot 2 \\cos 2t = \\frac{2 \\cos 2t}{\\sin 2t}\).
Now, use the chain rule to find \(\\frac{dy}{dx}\):
\(\\frac{dy}{dx} = \\frac{dy}{dt} \\div \\frac{dx}{dt} = \\frac{2 \\cos 2t}{\\sin 2t} \\div (2 - \\sec^2 t)\).
Simplify using trigonometric identities:
\(\\frac{dy}{dx} = \\frac{2 \\cos 2t}{\\sin 2t} \\cdot \\frac{1}{2 - \\sec^2 t}\).
Using the double angle formula, \(\\sin 2t = 2 \\sin t \\cos t\), and \(\\cos 2t = \\cos^2 t - \\sin^2 t\), we simplify:
\(\\frac{dy}{dx} = \\frac{\\cos t}{\\sin t} = \\cot t\).
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