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\frac{\mathrm{dy}}{\mathrm{dx}}=\frac{\mathrm{dy} / \mathrm{dt}}{\mathrm{dx} / \mathrm{dt}}=\frac{2 \mathrm{t}}{\cos (\mathrm{t})}=\frac{2 \cdot 2}{\cos (\mathbf{2})} \approx \frac{4}{-.42} \approx-9.61