Question

Is this answer correct:

Question: simplify the expression: cos(270degrees + x)

Answer: 0.762

Answer 1

I don't think so ..

Answer 2

Dont I use the sum difference formula?

Answer 3

No. There is a variable so it cannot be as the answer has to depend on x

Answer 4

I'll tell you one thing ... if you ever got values greater than 1 from Sin or Cos ... then you will always be wrong.

Answer 5

this is what I did, cos (theta + beta) = cos 270 cos x + sin270 sinx

Answer 6

then I get 0.975 + 0.2297

Answer 7

wait, I added something differently

Answer 8

cos(270+x) = - sin(x)

Answer 9

shouldnt the answer be 1.20?

Answer 10

OHHH! I see where I went wrong

Answer 11

I added intead of substracting

Answer 12

Shouldt the answer be 0.7462?

Answer 13

try this... use your graphing calculator (DEGREE mode, so change your x,y scale):
y1 = cos(270 + x)
y2 = -sin(x)
look at their graphs...

Answer 14

sorry,

sin(x) must be your answer ...stupid me

Answer 15

Im confused, -sinx or sinx?

Answer 16

oops
cos(270degrees + x)= cos(270)cos(x)-sin(270)sin(x)= +sin(x)

Answer 17

oh boy:)

Answer 18

ok. y2 = sinx
just going with the flow...

Answer 19

I take back saying Open did it correctly:
this is what I did, cos (theta + beta) = cos 270 cos x + sin270 sinx
should be cos 270 cos x - sin270 sinx

Answer 20

Thats what i said after:) I added instead of substract

Answer 21

now if you have a value for x, you can go further.

Answer 22

what they're trying to say is... you shouldn't be getting a numeric answer..
cos(270 + x) = sinx is an identity...

Answer 23

ok

Answer 24

try it out on your graphing calculator....

Answer 25

thats weird, when I graph it, I get like a line on opposite ends, and nothin in the middle

Answer 26

degree mode..

Answer 27

Yeah, It is on degree

Answer 28

window [-360, 360] for the x
[-2,2] for the y

Answer 29

ok, not I see it. I did something wrong with the zoom

Answer 30

I get waves in

Answer 31

I get waves in my graph

Answer 32

you only have equations in y1 and y2 only? nothing in the others?

Answer 33

yes, y1 = cos(270+x)
y2 = -sin(x)

Answer 34

y2 = sin(x)

Answer 35

Oh sorry, I tohught you said -sin(x) before, Ok Im chaging it

Answer 36

i did but i wsa just going with experinent and phi said....

Answer 37

So now I get like a wave starting in positive side and going up and down. Is this correct?

Answer 38

So basically, y1 and y2, will generate the same graph right?

Answer 39

Thats why it is an identity

Answer 40

the graph in y1 should be exactly on y2... that shows this is an identity.

Answer 41

yep

Answer 42

Here's what it should look like
http://www.wolframalpha.com/input/?i=plot%28cos%283pi%2F2%2Bx%29%29%2C+sin%28x%29

Answer 43

yeah thats the graph I got:)

Answer 44

Ok so backing it up a bit, when using the sum difference formulae

Answer 45

but look at what phi did on his earlier post... he actually proved cos(270+x) = sinx

Answer 46

How do I get that exactly?

Answer 47

I cant really put it in py calculator cause il get decimal answer

Answer 48

cos (270 + x) = cos 270 cos x - sin270 sinx

now find cos(270)=0
sin(270)=-1
so you get 0 - -sin(x) =sin(x) as your answer

Answer 49

Okok. that makes sense. Thank you so much guys:)

Answer 50

How were you getting a number out of this?

Answer 51

http://openstudy.com/study#/updates/4f8601bbe4b0505bf08604dc