Are these Trig problems correct?

[aaron9490]

If cos x = 3/5 and sin B = 5/13, x in quadrant 1, and B in quadrant 2, evaluate the following.


1. cos (X+B)

My answer: -36/65 - square root of 11/13

2. cos (X-B)

My answer: -36/65 + square root 11/13

3. sin (X+B)

My answer: -12 * square root of 11/65 + 3/13

4. sin (X-B)

My answer: -12 * square root of 11/65 - 3/13

5. tan (X+B)

My answer: square root of 11/3 + 5/-12 all over 1 - square root of 11/3 * 5/-12

6. tan (X-B)

My answer: square root of 11/3 - 5/-12 all over 1 - square root of 11/3 * 5/-12



Could someone tell me if any of these are wrong and what I did wrong. Thanks. Also, when I say "square root of 11" I mean that only the 11 is under the radical, no other number.

 

[tkhunny]

If cos x = 3/5 and sin B = 5/13, x in quadrant 1, and B in quadrant 2, evaluate the following.
1. cos (X+B)
My answer: -36/65 - square root of 11/13

Looks like you're missing something.

In Quadrant I, if cos(x) = 3/5, then sin(x) = 4/5.
In Quadrant II, if sin(B) = 5/13, then cos(x) = -12/13

cos(x+B) = cos(x)cos(B)-sin(x)sin(B)

Try it again.

 

[aaron9490]

Using that information and equation, I now get:


-36/65 - 12/13


If that is the right answer, is the second one wrong as well? Or was the first one the only one that was wrong?

 

[Deleted member 4993]

Using that information and equation, I now get:


-36/65 - 12/13


If that is the right answer, is the second one wrong as well? Or was the first one the only one that was wrong?

Show us your work - step-by-step - then we can tell you whether you are doing it correctly.