SOLUTION: Find the exact value of the expression: sin(4pi/9)cos(pi/9) - cos(4pi/9)sin(pi/9)

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Question 1137318: Find the exact value of the expression:
sin(4pi/9)cos(pi/9) - cos(4pi/9)sin(pi/9)
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850)   (Show Source): You can put this solution on YOUR website!



Use the following identity :


in your case and








Use the following identity :






Answer by ikleyn(52797)   (Show Source): You can put this solution on YOUR website!
.
Apply the formula for the sine of the arguments' difference 


sin(a-b) = sin(a)*cos(b) - cos(a)*sin(b).


You will get


 =  =  =  = .


Solved, answered and completed.



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