<PRE><B>Question 909400</B>
Using the exact value of the sine and the cosine of 1/6pi and 3/4pi and one of the sum and difference formulas, show that the exact value of sin(7/12pi) is 1/4(sqrt2+sqrt6)
 My answer is shown below but i get a minus not a plus: 
sin(7/12pi) = sin(3/4pi - 1/6pi)
 = sin(3/4pi)cos(1/6pi)-cos(3/4pi)sin(1/6pi)
Note: cos((3/4)pi) = (-1/2)sqrt(2)
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 ((1/2)(sqrt2))((1/2)(sqrt3)) - ((-1/2)sqrt2))(1/2)
 =1/4(sqrt6 + sqrt2) 
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Cheers,
Stan H. </PRE>