Question

what is sin (-13pi/4)
what is sin (-13pi/4)
@Mathematics

Answer 1

tyler can you help me with these two pls cos (
cos (5pi/3)
cos(-270 degrees)

and please show work

Answer 2

I can help you with the first one.

Answer 3

First, change \[- \frac{13 \pi}{4} \] into degrees to make things easy.

Answer 4

Do you know how to do that?

Answer 5

is it -13/4 times 180

Answer 6

Almost

Answer 7

\[- \frac{13 \pi}{4} * \frac{180}{\pi}\]

Answer 8

so we get -585 degrees?

Answer 9

So essentially yes because the pi's cancel.

Answer 10

Correct

Answer 11

ok what do we do with the degree

Answer 12

-585 is more than one revolution. So we can add a revolution (or 360 degrees) to -585

Answer 13

-585 + 360 = ?

Answer 14

-225

Answer 15

Good.

Answer 16

Now i like to deal with positive degrees. So to turn -225 into positive degrees. You do this \[-225 + 360\] Which is what?

Answer 17

135

Answer 18

Ok so saying \[\sin(- \frac{13\pi}{4})\] is like saying \[\sin(135)\] which is much easier to work with.

Answer 19

so thats the final answer, 135?

Answer 20

Well what is sin(135) ?

Answer 21

sqrt2/2

Answer 22

Correct!

Answer 23

awesome, why cant you help me with the other two...you explain better than my teacher lol

Answer 24

I can.. i wanted to start with the first one lol

Answer 25

ok kool

Answer 26

so for cos(5pi/3) we convert to degrees first right

Answer 27

ok so lets do \[\cos (\frac{5\pi}{3})\]

Answer 28

and get 300 degrees

Answer 29

Ok good.

Answer 30

do i do any subtraction...not sure

Answer 31

Well, you can.

Answer 32

so do i use 180 or 360

Answer 33

You should know what sin cos and tan of pi/3, pi/4 and pi/6 are.

Answer 34

So 300 is in the 4 th quadrant and you want a angle in the first so subtract 300 from 360

Answer 35

So \[\cos(300) = \cos(60)\]

Answer 36

and cos(60) is 1/2?

Answer 37

Now what is cos (60)? or pi/3

Answer 38

1/2?

Answer 39

Correct its 1/2

Answer 40

good stuff man

Answer 41

cos(-270) we add 360 and get 90 and cos 90 is 0?

Answer 42

now \[\cos(-270)\]

Answer 43

You got it!! You got the hang of it now!! :)

Answer 44

yeah thanks very much for the help

Answer 45

No problem.

Answer 46

ok i have another one

Find sin of angle if sin of angle < 0 and cos of angle = 2/3

Answer 47

1 and 4

Answer 48

ok

Answer 49

what do you mean

Answer 50

i see how the amplitude is one

Answer 51

how do i find the period