The parametric equations of a curve are
\(x = \frac{t}{2t + 3}\), \(y = e^{-2t}\).
Find the gradient of the curve at the point for which \(t = 0\).
Solution
To find the gradient \(\frac{dy}{dx}\), we first need to find \(\frac{dx}{dt}\) and \(\frac{dy}{dt}\).
For \(x = \frac{t}{2t + 3}\), use the quotient rule:
\(\frac{dx}{dt} = \frac{(2t + 3)(1) - t(2)}{(2t + 3)^2} = \frac{3}{(2t + 3)^2}\).
For \(y = e^{-2t}\), differentiate with respect to \(t\):
\(\frac{dy}{dt} = -2e^{-2t}\).
Now, use the chain rule to find \(\frac{dy}{dx}\):
\(\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{-2e^{-2t}}{\frac{3}{(2t + 3)^2}} = -2e^{-2t} \cdot \frac{(2t + 3)^2}{3}\).
Evaluate at \(t = 0\):
\(\frac{dy}{dx} = -2e^{0} \cdot \frac{3^2}{3} = -2 \cdot 3 = -6\).
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