find exact values for cos(x-y) if...

[vox]

Hi there

Just wanted to make sure i'm solving these problems correctly.

Q:
Find the exact values for a) cos(x-y) b) sin(x+y) .
If cosx=1/3, 0<x<180 and siny=-2/3, -90<y<90.

A:
a) (1/3)*(sqrt(5)/3)+(sqrt(8)/3)*(-2/3) =(sqrt(5)-2*sqrt(8))/9
b) (sqrt(8)/3)*(sqrt(5)/3)+(1/3)*(-2/3) = (sqrt(40)-2)/9

Thx
-V

 

[Ishuda]

Hi there

Just wanted to make sure i'm solving these problems correctly.

Q:
Find the exact values for a) cos(x-y) b) sin(x+y) .
If cosx=1/3, 0<x<180 and siny=-2/3, -90<y<90.

A:
a) (1/3)*(sqrt(5)/3)+(sqrt(8)/3)*(-2/3) =(sqrt(5)-2*sqrt(8))/9
b) (sqrt(8)/3)*(sqrt(5)/3)+(1/3)*(-2/3) = (sqrt(40)-2)/9

Thx
-V

Using one of our 'leaders' appropriate answer:

What are your thoughts?

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

http://www.freemathhelp.com/forum/announcement.php?f=33

 

[Steven G]

Hi there

Just wanted to make sure i'm solving these problems correctly.

Q:
Find the exact values for a) cos(x-y) b) sin(x+y) .
If cosx=1/3, 0<x<180 and siny=-2/3, -90<y<90.

A:
a) (1/3)*(sqrt(5)/3)+(sqrt(8)/3)*(-2/3) =(sqrt(5)-2*sqrt(8))/9
b) (sqrt(8)/3)*(sqrt(5)/3)+(1/3)*(-2/3) = (sqrt(40)-2)/9

Thx
-V

a is correct. For sqrt(8) I would put 2sqrt(2).

b is correct. For sqrt(40) put 2sqrt(10)

 

[vox]

Using one of our 'leaders' appropriate answer:

What are your thoughts?

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

http://www.freemathhelp.com/forum/announcement.php?f=33

The answers are from me, i'm just wondering if they're correct or not

a is correct. For sqrt(8) I would put 2sqrt(2).

b is correct. For sqrt(40) put 2sqrt(10)

Thank you

 

[Ishuda]

The answers are from me, i'm just wondering if they're correct or not

Sorry, I misread the problem. Something I've been telling others to do, so off to the corner for (sqrt(40)-2)/9 minutes

 

[Steven G]

Sorry, I misread the problem. Something I've been telling others to do, so off to the corner for (sqrt(40)-2)/9 minutes

OK, you can leave the corner now.