Question

I will give a medal! Trigonometry

Answer 1

@shaydoe Can you help?

Answer 2

yep

Answer 3

im not sure exactly sorry

Answer 4

@zepdrix Can you help me?

Answer 5

so we have f(x)=cos(x)
and we know f(-x)=cos(-x)=cos(x) since cos(x) is an even function

Answer 6

so you know f(x)=f(-x) for all x

Answer 7

that means you know f(-a) since you are given f(a)

Answer 8

for example cos(pi/4)=sqrt(2)/2 so cos(-pi/4) also equal sqrt(2)/2

Answer 9

so if cos(a)=2/7 then cos(-a)=?

Answer 10

well if you come back and I'm gone
a hint for the second question is cos has period 2pi

Answer 11

IM SO SORRY!!!!! @myininaya

Answer 12

cos(-a)= 2/7 since it's an even function

Answer 13

yep

Answer 14

For the second one what's changing is the period? So (a+ 2pi) means having a period of 4pi?

Answer 15

I'm confused

Answer 16

do you know that cos(pi/4)=sqrt(2)/2
and that cos(pi/4+2pi)=sqrt(2)/2
and that cos(pi/4+4pi)=sqrt(2)/2
and that cos(pi/4+2npi)=sqrt(2)/2
where n is an integer

Answer 17

so if cos(a)=2/7
then cos(a+2pi)=?

Answer 18

2/7. ohhhh so its like a reference angle

Answer 19

yeah
and cos(a+4pi) still equals

Answer 20

like it is like we are at a
and go all the way around to get back to a
so cos(a) is the same cos(a+2*pi*n) for an integer n

Answer 21

2/7 + 2/7 + 2/7 = 6/7?

Answer 22

yeah

Answer 23

I understand what your saying. Thanks a lot :) youre the best

Answer 24

:) np