- #1

hotrocks007

- 10

- 0

This one is due in a couple of hours, so any help would be appreciated!

If cos2t=1/3 and *0<_ 2t <_ pie, find cost. t=theta *less than or equal to

I dont know how to use the identities to help me.

Please help!

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter hotrocks007
- Start date

- #1

hotrocks007

- 10

- 0

This one is due in a couple of hours, so any help would be appreciated!

If cos2t=1/3 and *0<_ 2t <_ pie, find cost. t=theta *less than or equal to

I dont know how to use the identities to help me.

Please help!

- #2

Jameson

Gold Member

MHB

- 4,538

- 13

[tex]\cos{(2\alpha)} = 2\cos^2{(\alpha)}-1[/tex]

Plug that in and post when you make progress.

- #3

hotrocks007

- 10

- 0

ohh, costheta=sqrt(6)/3

?

?

- #4

Jameson

Gold Member

MHB

- 4,538

- 13

[tex]2\cos^2{(\alpha)}=\frac{4}{3}[/tex]

[tex]\cos^2{(\alpha)}=\frac{2}{3}[/tex]

Can you finish from here?

- #5

hotrocks007

- 10

- 0

how about this one.

I'm not sure how to simplify it down, and how to distribute the ^2 once it has been plugged in.

x^2 + y^2 +3x=0 when x=rcostheta and y=rsintheta

- #6

Nylex

- 552

- 2

- #7

Jameson

Gold Member

MHB

- 4,538

- 13

[tex](r\cos{\theta})^2 + (r\sin{\theta})^2+3(r\cos{\theta})=0[/tex]

[tex]r^2\cos^2{(\theta)}+r^2\sin^2{(\theta)}+3(r\cos{\theta})=0[/tex]

Do you see the trig identity coming in?

[tex]r^2\cos^2{(\theta)}+r^2\sin^2{(\theta)}+3(r\cos{\theta})=0[/tex]

Do you see the trig identity coming in?

Last edited by a moderator:

- #8

hotrocks007

- 10

- 0

the Pythag. Identity? Would you have to plug in rcostheta with the 3x?

- #9

Jameson

Gold Member

MHB

- 4,538

- 13

I'll give you my last hint to this problem.

[tex]r^2\cos^2{(\theta)}+r^2\sin^2{(\theta)}+3(r\cos{\theta})=0[/tex]

[tex]r^2(\cos^2{\theta}+\sin^2{\theta})...[/tex]

- #10

hotrocks007

- 10

- 0

OH! thanks!!!!!

- #11

hotrocks007

- 10

- 0

when you distribute the 3, would it be 3rcos3theta? or do you just not distribute the 3 to the cos?

- #12

Jameson

Gold Member

MHB

- 4,538

- 13

[tex]3r\cos{(\theta)}[/tex]

Share:

- Last Post

- Replies
- 4

- Views
- 489

- Last Post

- Replies
- 8

- Views
- 342

- Replies
- 2

- Views
- 435

- Last Post

- Replies
- 2

- Views
- 419

- Last Post

- Replies
- 3

- Views
- 407

- Last Post

- Replies
- 3

- Views
- 829

- Replies
- 2

- Views
- 1K

- Last Post

- Replies
- 5

- Views
- 765

- Replies
- 30

- Views
- 2K

- Last Post

- Replies
- 1

- Views
- 486