Question

Find the exact value of each o the following expressions using trigonometric sum identities

cos75 degrees

sin195 degrees

tan105 degrees

Answer 1

cos .2588

sin -.2588

tan -3.7

Answer 2

how?

Answer 3

That's just my calculator I don't know what they mean by trigonometric sum identities.

Answer 4

Thanks then:)

Answer 5

here i'll look it up

Answer 6

this might help you https://www.youtube.com/watch?v=ImUluLTJFno

Answer 7

yeah it helped with the first one

Answer 8

HI!!

Answer 9

you are supposed to use the addition angle formula for this one

Answer 10

\[75^\circ=30^\circ+45^\circ\]
and \[\cos(a+b)=\cos(a)\cos(b)-\sin(a)\sin(b)\]

Answer 11

put in \(a=30^\circ\)and \(b=45^\circ\)
compute the result

Answer 12

Yes I have solved that one and I kinda understand but once it gets to using the unit circle I am a little lost

Answer 13

you need to know how to find \(\cos(30)\) and so on?

Answer 14

On the unit circle, yes

Answer 15

find the point corresponding to the angle of 30 on the unit circle
let me know when you are looking at \((\frac{\sqrt3}{2}, \frac{1}{2})\)

Answer 16

yes, okay that helps me a lot!!! thanks for that

Answer 17

the first coordinate is cosine , the second is sine

Answer 18

so \[\cos(30)=\frac{\sqrt3}{2}\]and \[\sin(30)=\frac{1}{2}\]

Answer 19

okay so I see that I just plug those in and then simplify.

Answer 20

yes

Answer 21

For the second one I dont know if I should use sin(a-b) or sin(a+b)

Answer 22

and I know its 195, so should I do 180+15?
Or should I use 210-15?

Answer 23

@misty1212

Answer 24

@jim_thompson5910 can you help me?