Question

HELP PLEASE!!!!
Use a Sum or Difference Identity to evaluate sin 165°.

Answer 1

well what two things when added would give you 165 degree's and ALSO that those two numbers would be degrees that you know on the unit circle?

Answer 2

sin 165 = sin (120 + 45) = sin120cos45 + cos120sin45

sin 120 = sqrt3/2, cos 120 = -1/2
sin 45 = cos45 = 1/sqrt2

Answer 3

120 and 45

Answer 4

yea - thats what i used

Answer 5

now do i just sub

Answer 6

yes sub those values in right hand side of the identity

Answer 7

Yup, you can then just sub it in and carry out the calculations easy since they're on the unit circle. Here's a trig reference sheet i made too: http://learnix.net/wordpress/wp-content/uploads/Trig-Cheat-Sheet-1.4.pdf

Answer 8

\[\sqrt{2}+\sqrt{6}/4\]
\[\sqrt{6}-\sqrt{2}/4\]
1/2
-1

Answer 9

which one is it??

Answer 10

i likt that reference sheet - really comprehensive

Answer 11

@cwrw238 Thanks! :D

Answer 12

@agentc0re or @cwrw238 which choice would u pick from what i posted??

Answer 13

well i can't just give you the answer. :D What did you calculate?

Answer 14

i got \[\sqrt{3}-1/2\sqrt{2}\]
but thats nonw of my choices

Answer 15

you're answer is correct. So they've done something, or did do something(simplify) to get the answers that they are giving you.

That's a little annoying... Um, Multiply the answer by:
\[\large \sqrt2 \over \sqrt2\]

Answer 16

\[\sqrt{6}-\sqrt{2}/4\]

Answer 17

now look at your answers. :D

Answer 18

err answer choices. :D

Answer 19

wait im wrong??

Answer 20

No, you're right. it's also one of your answer choices. :D

Answer 21

oh ok could u also help me with a few others??

Answer 22

Did you download my reference sheet?

Answer 23

yes y ?.

Answer 24

@agentc0re r u there??

Answer 25

i am.

Answer 26

If sin =3/5 , find sin 2theta given that θ is in the 3rd quadrant.