Homework Help: trig

Posted by Natash on Saturday, November 15, 2008 at 2:40am.

Give exact answers
Sin(11pi/8)
so this is sin(pi/4+pi/3)
sin(pi/4)*cos(pi/3)+cos(pi/3)*sin(pi/4)
rad2/2*1/2+1/2*rad2/2

which gives me rad2+rad2 all over 4 ...i dont know y im getting it wrong

trig - drwls, Saturday, November 15, 2008 at 5:09am
pi/4 + pi/3 does NOT equal 11 pi/8
It equals 7 pi/12

sin (11pi/8) = -sin3pi/8
= -sin[(1/2)3pi/4]
Now use the "sine half angle" formula
= -sqrt[(1/2)(1-cos3pi/4)]
= -sqrt[(1/2)(1+(sqrt2)/2)]

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