Question

Use a sum or difference equation to find the exact value of the following:
sin(7pi/18) cos(2pi/9) - cos(7pi/18) sin(2pi/9)
PLEASE HELP ME

Answer 1

sum or difference *formula

Answer 2

\(\normalsize\color{darkgreen}{ \rm cos~(~7π/18~-~2π/9~) }\) tell me what you get when you expand it to verify, but for now, I'll simplify this answer even more

Answer 3

you can't expand it because 110 is not divisible by 15

Answer 4

is cos(110) the answer then?

Answer 5

sorry, I made an error

Answer 6

I got cos(110) correctly,but

Answer 7

\(\normalsize\color{darkgreen}{ \rm cos~(7π/18 + 2π/9) }\)

Answer 8

shouldn't it be sin instead of cos

Answer 9

\(\normalsize\color{darkgreen}{ \rm cos~(7π/18 - 2π/9) }\)

Answer 10

\(\normalsize\color{darkgreen}{ \rm cos~(7π/18 - 4π/18) }\)
\(\normalsize\color{darkgreen}{ \rm cos~(3π/18) }\)
\(\normalsize\color{darkgreen}{ \rm cos~(30) }\)