Calculus 2 : Parametric, Polar, and Vector

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #12 : Polar

What is the equation \(\displaystyle y=\frac{2}{3}x^{2}\) in polar form?

Possible Answers:

\(\displaystyle r=\frac{3}{2}\tan \theta\sec\theta\)

None of the above

\(\displaystyle r=\frac{2}{3}\tan \theta\sec\theta\)

\(\displaystyle r=-\frac{3}{2}\tan \theta\sec\theta\)

\(\displaystyle r=-\frac{2}{3}\tan \theta\sec\theta\)

Correct answer:

\(\displaystyle r=\frac{3}{2}\tan \theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: \(\displaystyle y=r\sin\theta\) and \(\displaystyle x=r\cos\theta\). Given \(\displaystyle y=\frac{2}{3}x^{2}\), then:

\(\displaystyle r\sin\theta=\frac{2}{3}(r\cos \theta)^{2}\)

\(\displaystyle r\sin\theta=\frac{2}{3}r^{2}\cos^{2} \theta\)

 Dividing both sides by \(\displaystyle r\cos\theta\), we get:

\(\displaystyle \tan \theta=\frac{2}{3}r\cos\theta\)

\(\displaystyle \frac{\tan \theta}{\cos\theta}=\frac{2}{3}r\)

\(\displaystyle 3\tan \theta\sec\theta=2r\)

\(\displaystyle r=\frac{3}{2}\tan \theta\sec\theta\)

Example Question #181 : Parametric, Polar, And Vector

What is the polar form of \(\displaystyle y=\frac{3}{5}x^{2}\)?

Possible Answers:

None of the above

\(\displaystyle r=-\frac{3}{5}\tan\theta\sec\theta\)

\(\displaystyle r=\frac{5}{3}\tan\theta\sec\theta\)

\(\displaystyle r=\frac{3}{5}\tan\theta\sec\theta\)

\(\displaystyle r=-\frac{5}{3}\tan\theta\sec\theta\)

Correct answer:

\(\displaystyle r=\frac{5}{3}\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=\frac{3}{5}x^{2}\), then:

\(\displaystyle r\sin\theta=\frac{3}{5}(r\cos\theta)^{2}\)

\(\displaystyle r\sin\theta=\frac{3}{5}r^{2}\cos^{2}\theta\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=\frac{3}{5}r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=\frac{3}{5}r\)

\(\displaystyle \tan\theta\sec\theta=\frac{3}{5}r\)

\(\displaystyle r=\frac{5}{3}\tan\theta\sec\theta\)

 

Example Question #12 : Polar

What is the polar form of \(\displaystyle y=-7x^{2}\)?

Possible Answers:

\(\displaystyle r=-7\tan\theta\sec\theta\)

\(\displaystyle r=-\frac{1}{7}\tan\theta\sec\theta\)

\(\displaystyle r=\frac{1}{7}\tan\theta\sec\theta\)

\(\displaystyle r=\tan7\theta\sec\theta\)

\(\displaystyle r=7\tan\theta\sec\theta\)

Correct answer:

\(\displaystyle r=-\frac{1}{7}\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=-7x^{2}\), then:

\(\displaystyle r\sin\theta=-7(r\cos\theta)^{2}\)

\(\displaystyle r\sin\theta=-7r^{2}\cos^{2}\theta\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=-7r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=-7r\)

\(\displaystyle \tan\theta\sec\theta=-7r\)

\(\displaystyle r=-\frac{1}{7}\tan\theta\sec\theta\)

Example Question #12 : Polar Form

What is the polar form of \(\displaystyle y=\frac{1}{2}x^{2}\)?

Possible Answers:

\(\displaystyle r=-2\tan\theta\sec\theta\)

\(\displaystyle r=\frac{1}{2}\tan\theta\sec\theta\)

None of the above

\(\displaystyle r=-\frac{1}{2}\tan\theta\sec\theta\)

\(\displaystyle r=2\tan\theta\sec\theta\)

Correct answer:

\(\displaystyle r=2\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=\frac{1}{2}x^{2}\), then:

\(\displaystyle r\sin\theta=\frac{1}{2}(r\cos\theta)^{2}\)

\(\displaystyle r\sin\theta=\frac{1}2{}\cos^{2}\theta\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=\frac{1}{2}r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=\frac{1}{2}r\)

\(\displaystyle \tan\theta\sec\theta=\frac{1}{2}r\)

\(\displaystyle r=2\tan\theta\sec\theta\)

Example Question #21 : Polar

What is the polar form of \(\displaystyle y=4x^{2}\)?

Possible Answers:

\(\displaystyle r=-4\tan\theta\sec\theta\)

\(\displaystyle r=-4\tan\theta\sec\theta\)

\(\displaystyle r=\frac{1}{4}\tan\theta\sec\theta\)

\(\displaystyle r=-\frac{1}{4}\tan\theta\sec\theta\)

\(\displaystyle r=\tan4\theta\sec\theta\)

Correct answer:

\(\displaystyle r=\frac{1}{4}\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=4x^{2}\), then:

\(\displaystyle r\sin\theta=4(r\cos\theta)^{2}\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=4r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=4r\)

\(\displaystyle \tan\theta\sec\theta=4r\)

\(\displaystyle r=\frac{1}{4}\tan\theta\sec\theta\)

 

 

Example Question #7 : Polar Form

What is the polar form of \(\displaystyle y=-x^{2}\)?

Possible Answers:

\(\displaystyle r=\tan\theta\sec\theta\)

\(\displaystyle r=\frac{\tan\theta}{\sec\theta}\)

None of the above

\(\displaystyle r=-\frac{\tan\theta}{\sec\theta}\)

\(\displaystyle r=-\tan\theta\sec\theta\)

Correct answer:

\(\displaystyle r=-\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=-x^{2}\), then:

\(\displaystyle r\sin\theta=-(r\cos\theta)^{2}\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=-r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=-r\)

\(\displaystyle \tan\theta\sec\theta=-r\)

\(\displaystyle r=-\tan\theta\sec\theta\)

Example Question #13 : Polar Form

What is the polar form of \(\displaystyle y=\frac{1}{6}x^{2}\)?

Possible Answers:

\(\displaystyle r=\frac{\tan\theta}{6\sec\theta}\)

\(\displaystyle r=\frac{1}{6}\tan\theta\sec\theta\)

\(\displaystyle r=-6\tan\theta\sec\theta\)

\(\displaystyle r=-\frac{1}{6}\tan\theta\sec\theta\)

\(\displaystyle r=6\tan\theta\sec\theta\)

Correct answer:

\(\displaystyle r=6\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=\frac{1}{6}x^{2}\), then:

\(\displaystyle r\sin\theta=\frac{1}{6}(r\cos\theta)^{2}\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=\frac{1}{6}r\cos\theta\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=\frac{1}{6}r\)

\(\displaystyle \tan\theta\sec\theta=\frac{1}{6}r\)

\(\displaystyle r=6\tan\theta\sec\theta\)

Example Question #21 : Polar

What is the polar form of \(\displaystyle y=\frac{5}{3}x^{2}\)?

Possible Answers:

\(\displaystyle r=-\frac{3}{5}\tan\theta\sec\theta\)

\(\displaystyle r=\frac{5}{3}\tan\theta\sec\theta\)

\(\displaystyle r=\frac{3}{5}\tan\theta\sec\theta\)

\(\displaystyle r=-\frac{5}{3}\tan\theta\sec\theta\)

None of the above

Correct answer:

\(\displaystyle r=\frac{3}{5}\tan\theta\sec\theta\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=\frac{5}{3}x^{2}\), then:

\(\displaystyle r\sin\theta=\frac{5}{3}(r\cos\theta)^{2}\)

Dividing both sides by , we get:

\(\displaystyle \tan\theta=\frac{5}{3}(r\cos\theta)\)

\(\displaystyle \frac{\tan\theta}{\cos\theta}=\frac{5}{3}r\)

\(\displaystyle \tan\theta\sec\theta=\frac{5}{3}r\)

\(\displaystyle r=\frac{3}{5}\tan\theta\sec\theta\)

Example Question #21 : Polar Form

What is the polar form of \(\displaystyle y=2x-1\)?

Possible Answers:

\(\displaystyle r=\frac{1}{\sin\theta-2\cos\theta}\)

\(\displaystyle r=\frac{1}{\sin\theta+2\cos\theta}\)

\(\displaystyle r=-\frac{1}{\sin\theta+2\cos\theta}\)

\(\displaystyle r=-\frac{1}{\sin\theta-2\cos\theta}\)

None of the above

Correct answer:

\(\displaystyle r=-\frac{1}{\sin\theta-2\cos\theta}\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=2x-1\), then:

\(\displaystyle r\sin\theta=2(r\cos\theta)-1\)

\(\displaystyle r\sin\theta-2(r\cos\theta)=-1\)

\(\displaystyle r\sin\theta-2(r\cos\theta)=-1\)

\(\displaystyle r(\sin\theta-2\cos\theta)=-1\)

\(\displaystyle r=-\frac{1}{\sin\theta-2\cos\theta}\)

 

 

Example Question #6 : Polar Form

What is the polar form of \(\displaystyle y=3-4x\)?

Possible Answers:

\(\displaystyle r=-\frac{3}{\sin\theta+4\cos\theta}\)

\(\displaystyle r=-\frac{3}{\sin\theta-4\cos\theta}\)

\(\displaystyle r=\frac{3}{\sin\theta+4\cos\theta}\)

None of the above

\(\displaystyle r=\frac{3}{\sin\theta-4\cos\theta}\)

Correct answer:

\(\displaystyle r=\frac{3}{\sin\theta+4\cos\theta}\)

Explanation:

We can convert from rectangular to polar form by using the following trigonometric identities: and . Given \(\displaystyle y=3-4x\), then:

\(\displaystyle r\sin\theta=3-4(r\cos\theta)\)

\(\displaystyle r\sin\theta+4(r\cos\theta)=3\)

\(\displaystyle r(\sin\theta+4\cos\theta)=3\)

\(\displaystyle r=\frac{3}{\sin\theta+4\cos\theta}\)

 

 

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