document.write( "Question 909400: 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)\r
\n" ); document.write( "\n" ); document.write( "My answer is shown below but i get a minus not a plus:\r
\n" ); document.write( "\n" ); document.write( "sin(7/12pi) = sin(3/4pi - 1/6pi)
\n" ); document.write( "sin(3/4pi)cos(1/6pi)-cos(3/4pi)sin(1/6pi)
\n" ); document.write( "(1/2sqrt2)(1/2sqrt3) - (1/2sqrt2)(1/2)
\n" ); document.write( "=1/4(sqrt6 - sqrt2) but it needs to be plus not minus can you please tell me where i'm going wrong? Many thanks \n" ); document.write( "

Algebra.Com's Answer #551876 by stanbon(75887) $\"\"$ $\"About$

You can put this solution on YOUR website!
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)
\n" ); document.write( " My answer is shown below but i get a minus not a plus:
\n" ); document.write( "sin(7/12pi) = sin(3/4pi - 1/6pi)
\n" ); document.write( " = sin(3/4pi)cos(1/6pi)-cos(3/4pi)sin(1/6pi)
\n" ); document.write( "Note: cos((3/4)pi) = (-1/2)sqrt(2)
\n" ); document.write( "------------------
\n" ); document.write( " ((1/2)(sqrt2))((1/2)(sqrt3)) - ((-1/2)sqrt2))(1/2)
\n" ); document.write( " =1/4(sqrt6 + sqrt2)
\n" ); document.write( "---------
\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H. \n" ); document.write( "

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