- #1

- 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!

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- Thread starter hotrocks007
- Start date

- #1

- 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

- 793

- 4

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

Plug that in and post when you make progress.

- #3

- 10

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ohh, costheta=sqrt(6)/3

?

?

- #4

- 793

- 4

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

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

Can you finish from here?

- #5

- 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

- 551

- 1

- #7

- 793

- 4

[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:

- #8

- 10

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

- #9

- 793

- 4

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

- 10

- 0

OH! thanks!!!!!

- #11

- 10

- 0

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

- #12

- 793

- 4

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

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