If the parametric equation of a curve is given by $x=e^t cost$ and $y=e^t sint$ then the tangent to the curve at the point $t=\frac{\pi}{4}$ makes the angle with the axis of x is
$$x = e^t \cos t,\quad y = e^t \sin t$$
To find the angle of the tangent at \( t = \frac{\pi}{4} \), compute the slope:
$$\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{e^t(\sin t + \cos t)}{e^t(\cos t - \sin t)} = \frac{\sin t + \cos t}{\cos t - \sin t}$$
At \( t = \frac{\pi}{4} \),
$$\sin\left(\frac{\pi}{4}\right) = \cos\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}$$
So,
$$\frac{dy}{dx} = \frac{\frac{\sqrt{2}}{2} + \frac{\sqrt{2}}{2}}{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}} = \frac{\sqrt{2}}{0}$$
The slope is undefined, which means the tangent is vertical.
Final Answer: The angle with the x-axis is
$$\boxed{90^\circ}$$
[{"qus_id":"11691","year":"2024"}]
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