<< Chapter < Page Chapter >> Page >

Converting a conic in polar form to rectangular form

Convert the conic r = 1 5 5 sin θ to rectangular form.

We will rearrange the formula to use the identities   r = x 2 + y 2 , x = r cos θ , and  y = r sin θ .

                           r = 1 5 5 sin θ   r ( 5 5 sin θ ) = 1 5 5 sin θ ( 5 5 sin θ ) Eliminate the fraction .         5 r 5 r sin θ = 1 Distribute .                          5 r = 1 + 5 r sin θ Isolate  5 r .                      25 r 2 = ( 1 + 5 r sin θ ) 2 Square both sides .           25 ( x 2 + y 2 ) = ( 1 + 5 y ) 2 Substitute  r = x 2 + y 2  and  y = r sin θ .         25 x 2 + 25 y 2 = 1 + 10 y + 25 y 2 Distribute and use FOIL .           25 x 2 10 y = 1 Rearrange terms and set equal to 1 .
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Convert the conic r = 2 1 + 2   cos   θ to rectangular form.

4 8 x + 3 x 2 y 2 = 0

Got questions? Get instant answers now!

Access these online resources for additional instruction and practice with conics in polar coordinates.

Visit this website for additional practice questions from Learningpod.

Key concepts

  • Any conic may be determined by a single focus, the corresponding eccentricity, and the directrix. We can also define a conic in terms of a fixed point, the focus P ( r , θ ) at the pole, and a line, the directrix, which is perpendicular to the polar axis.
  • A conic is the set of all points e = P F P D , where eccentricity e is a positive real number. Each conic may be written in terms of its polar equation. See [link] .
  • The polar equations of conics can be graphed. See [link] , [link] , and [link] .
  • Conics can be defined in terms of a focus, a directrix, and eccentricity. See [link] and [link] .
  • We can use the identities r = x 2 + y 2 , x = r   cos   θ , and y = r   sin   θ to convert the equation for a conic from polar to rectangular form. See [link] .

Section exercises

Verbal

Explain how eccentricity determines which conic section is given.

If eccentricity is less than 1, it is an ellipse. If eccentricity is equal to 1, it is a parabola. If eccentricity is greater than 1, it is a hyperbola.

Got questions? Get instant answers now!

If a conic section is written as a polar equation, what must be true of the denominator?

Got questions? Get instant answers now!

If a conic section is written as a polar equation, and the denominator involves sin   θ , what conclusion can be drawn about the directrix?

The directrix will be parallel to the polar axis.

Got questions? Get instant answers now!

If the directrix of a conic section is perpendicular to the polar axis, what do we know about the equation of the graph?

Got questions? Get instant answers now!

What do we know about the focus/foci of a conic section if it is written as a polar equation?

One of the foci will be located at the origin.

Got questions? Get instant answers now!

Algebraic

For the following exercises, identify the conic with a focus at the origin, and then give the directrix and eccentricity.

r = 6 1 2   cos   θ

Got questions? Get instant answers now!

r = 3 4 4   sin   θ

Parabola with e = 1 and directrix 3 4 units below the pole.

Got questions? Get instant answers now!

r = 8 4 3   cos   θ

Got questions? Get instant answers now!

r = 5 1 + 2   sin   θ

Hyperbola with e = 2 and directrix 5 2 units above the pole.

Got questions? Get instant answers now!

r = 16 4 + 3   cos   θ

Got questions? Get instant answers now!

r = 3 10 + 10   cos   θ

Parabola with e = 1 and directrix 3 10 units to the right of the pole.

Got questions? Get instant answers now!

r = 4 7 + 2   cos   θ

Ellipse with e = 2 7 and directrix 2 units to the right of the pole.

Got questions? Get instant answers now!

r ( 1 cos   θ ) = 3

Got questions? Get instant answers now!

r ( 3 + 5 sin   θ ) = 11

Hyperbola with e = 5 3 and directrix 11 5 units above the pole.

Got questions? Get instant answers now!

r ( 4 5 sin   θ ) = 1

Got questions? Get instant answers now!

r ( 7 + 8 cos   θ ) = 7

Hyperbola with e = 8 7 and directrix 7 8 units to the right of the pole.

Got questions? Get instant answers now!

Questions & Answers

can I see the picture
Zairen Reply
How would you find if a radical function is one to one?
Peighton Reply
how to understand calculus?
Jenica Reply
with doing calculus
SLIMANE
Thanks po.
Jenica
Hey I am new to precalculus, and wanted clarification please on what sine is as I am floored by the terms in this app? I don't mean to sound stupid but I have only completed up to college algebra.
rachel Reply
I don't know if you are looking for a deeper answer or not, but the sine of an angle in a right triangle is the length of the opposite side to the angle in question divided by the length of the hypotenuse of said triangle.
Marco
can you give me sir tips to quickly understand precalculus. Im new too in that topic. Thanks
Jenica
if you remember sine, cosine, and tangent from geometry, all the relationships are the same but they use x y and r instead (x is adjacent, y is opposite, and r is hypotenuse).
Natalie
it is better to use unit circle than triangle .triangle is only used for acute angles but you can begin with. Download any application named"unit circle" you find in it all you need. unit circle is a circle centred at origine (0;0) with radius r= 1.
SLIMANE
What is domain
johnphilip
the standard equation of the ellipse that has vertices (0,-4)&(0,4) and foci (0, -15)&(0,15) it's standard equation is x^2 + y^2/16 =1 tell my why is it only x^2? why is there no a^2?
Reena Reply
what is foci?
Reena Reply
This term is plural for a focus, it is used for conic sections. For more detail or other math questions. I recommend researching on "Khan academy" or watching "The Organic Chemistry Tutor" YouTube channel.
Chris
how to determine the vertex,focus,directrix and axis of symmetry of the parabola by equations
Bryssen Reply
i want to sure my answer of the exercise
meena Reply
what is the diameter of(x-2)²+(y-3)²=25
Den Reply
how to solve the Identity ?
Barcenas Reply
what type of identity
Jeffrey
Confunction Identity
Barcenas
how to solve the sums
meena
hello guys
meena
For each year t, the population of a forest of trees is represented by the function A(t) = 117(1.029)t. In a neighboring forest, the population of the same type of tree is represented by the function B(t) = 86(1.025)t.
Shakeena Reply
by how many trees did forest "A" have a greater number?
Shakeena
32.243
Kenard
how solve standard form of polar
Rhudy Reply
what is a complex number used for?
Drew Reply
It's just like any other number. The important thing to know is that they exist and can be used in computations like any number.
Steve
I would like to add that they are used in AC signal analysis for one thing
Scott
Good call Scott. Also radar signals I believe.
Steve
They are used in any profession where the phase of a waveform has to be accounted for in the calculations. Imagine two electrical signals in a wire that are out of phase by 90°. At some times they will interfere constructively, others destructively. Complex numbers simplify those equations
Tim
Is there any rule we can use to get the nth term ?
Anwar Reply
how do you get the (1.4427)^t in the carp problem?
Gabrielle Reply
Practice Key Terms 2

Get the best Precalculus course in your pocket!





Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Precalculus' conversation and receive update notifications?

Ask