Question

Find a cartesian equation for the curve and identify it. r = 10 tan(θ) sec(θ)

Answer 1

For a cartesian equation
$x=r\cos\theta \ and \ y=r\sin\theta \\ \\ \cos\theta=\frac{x}{r} \ and \ \sin\theta=\frac{y}{r} \\ \\ \tan\theta=\frac{\sin\theta}{\cos\theta}=\frac{y}{r}\cdot\frac{r}{x}=\frac{y}{x} \\ \\ \sec\theta=\frac{1}{\cos\theta}=\frac{r}{x}$

Given r = 10 tan(θ) sec(θ)
$r=10\tan\theta\sec\theta=10\cdot\frac{y}{x}\cdot\frac{r}{x} \\ \\ \Rightarrow10y=x^2 \\ \\ \Rightarrow y= \frac{1}{10} x^2$

Therefore,the curve is a parabola opening upward with vertex (0, 0).