Question

cos80cos20+sin80sin20

Answer 1

hint:

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

Answer 2

cos80+20

Answer 3

let x = 80, y = 20

Answer 4

then what

Answer 5

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

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

cos(80)cos(20) + sin(80)sin(20) = cos(80-20)

cos(80)cos(20) + sin(80)sin(20) = ???

Answer 6

so cos 80+20

Answer 7

what does cos(80-20) turn into

Answer 8

cos60

Answer 9

and what does cos(60) evaluate to?

Answer 10

\[\sqrt{2}/\]

Answer 11

no

Answer 12

2

Answer 13

that's cos(45)

Answer 14

1/2

Answer 15

yep

Answer 16

cos(80)cos(20) + sin(80)sin(20) = cos(60)

cos(80)cos(20) + sin(80)sin(20) = 1/2

Answer 17

since i have you here can i ask you how to do \[\cos(2\sin^{-1} (-3\div5)\]

Answer 18

i got -1/2 as the answer was i doing something right or just way off

Answer 19

-1/2 is incorrect

Answer 20

what do i do

Answer 21

after the identity what is the next step

Answer 22

i did so can i just swap the sin with the cos fractions

Answer 23

4

Answer 24

so the answer would be 4/5

Answer 25

idk why but I've been doing this all wrong...

Answer 26

let me fix it

Answer 27

cos(2*arcsin(-3/5))


cos(2x)


2*cos^2(x) - 1


2*(4/5)^2 - 1


2*(16/25) - 1


32/25 - 1


32/25 - 25/25


7/25

Answer 28

So,

cos(2*arcsin(-3/5)) = 7/25

Answer 29

thank you the 25/25 was pi correct?

Answer 30

o sorry it was the 1

Answer 31

pi?