Question

Help with trigonometry identities please!

Simplify:
a) cos(180º +x) + cos(180º - x)
b) cos(7pi/126º)cos(36º/5)+sin(7pi/126º)sin(36º/5)

Answer 1

cos(a+b) - cos(a-b):

cos^2(a) - sin^2(a) + cos^2(a) + sin^2(a)

2cos^2(a)

2cos^2(180) ; cos(180) = -1

2(-1^2) = 2(1) = 2

Answer 2

\[7\pi/126^O\] ????

Answer 3

if anything that would equal 7pi(180)/126pi ... but ive never seen anything written like that before.

Answer 4

this is the equation:

Answer 5

well, its a cos(a-b) construct, but i dunno about those digits

Answer 6

if you convert the degrees to radians, then I spoose you can have a radian measure without a pi in it.... but its just unnatural :)

Answer 7

ok..thanks for the help on the first one

Answer 8

7pi = 180 degrees, lets substitute that in instead

Answer 9

cos(180/126)cos(36/5) + sin(180/126º)sin(36/5)

Answer 10

then

cos(180/126 - 36/5) is your angle....

Answer 11

add the fractions and simplify... right?

Answer 12

3636
-----
630

Answer 13

602/105...whats our remainder?

Answer 14

did u already multiply the fraction by cos? im confused, sorry :S

Answer 15

5 + (77/105)

Answer 16

you dont need to do that :) you just need to find the angle of the cos:

cos(a - b); find a - b

Answer 17

108(5) 36(126)
------ - --------
126(5) 126(5)

Answer 18

180(5) 36(126)
------ - --------
126(5) 126(5)

arghh!!..typoed it lol

Answer 19

3636
cos of ----- is what I get
630

Answer 20

-3636
------ you gotta catch this stuff, cause I dont always ;)
630

Answer 21

Amistre please help :'(

Answer 22

that looked alot better in my head lol

Answer 23

loco..... give me a sec; im on break ;)

Answer 24

ok

Answer 25

im not about to catch anything lol. i am very confused by trig in general..im about to post a question on trig identities...could u maybe help me through those when i post it? u seem like u know what ur doing :)

Answer 26

its a farse, I no nutheeenng!!!

Answer 27

he does. he know his stuff :)

Answer 28

ur a superhero for a reason :)

Answer 29

pfftt!!!.....super hero, now I gotta wear tights, and that aint a pretty picture ;)

Answer 30

I get an angle of -5.77 degrees when we do all that.

Answer 31

that is if its even right lol

Answer 32

the cos of that angle = .9949 and thats the best I got fer ya on that one....right or wrong ;)

Answer 33

r u solving the whole question btw? i just need to simplify..

Answer 34

I solved it for the angle; andle = 5 + (77/105)

and for the value of the cosine of that angle :=: .9949

how to simplify it is beyond me :)

Answer 35

:'( ok. that's better than no answer at least!

Answer 36

well, -5 and 77/105ths.... but yeah :) ..good luck with it; if anything, get it wrong and move ahead :)