Sunday, May 11, 2008

`-(7pi)/12` Find the exact values of the sine, cosine, and tangent of the angle.

`sin((-7pi)/12)=-sin((7pi)/12)`


`=-sin(pi/3+pi/4)`


using the identity `sin(x+y)=sin(x)cos(y)+cos(x)sin(y)`


`=-(sin(pi/3)cos(pi/4)+cos(pi/3)sin(pi/4))`


`=-(sqrt(3)/2*1/sqrt(2)+1/2*1/sqrt(2))`


`=-(sqrt(3)+1)/(2sqrt(2))`


rationalizing the denominator,


`=(-sqrt(2)(sqrt(3)+1))/4`


`cos((-7pi)/12)=cos((7pi)/12)`


`=cos(pi/3+pi/4)`


using the identity `cos(x+y)=cos(x)cos(y)-sin(x)sin(y)`


`=cos(pi/3)cos(pi/4)-sin(pi/3)sin(pi/4)`


`=(1/2*1/sqrt(2)-sqrt(3)/2*1/sqrt(2))`


`=(1-sqrt(3))/(2sqrt(2))`


rationalizing the denominator,


`=(sqrt(2)(1-sqrt(3)))/4`


`=(sqrt(2)-sqrt(6))/4`


`tan((-7pi)/12)`


`=sin((-7pi)/12)/cos((-7pi)/12)`


plug in the values evaluated above,


`=((-sqrt(2)(sqrt(3)+1))/4)/((sqrt(2)-sqrt(6))/4)`


`=(-sqrt(2)(sqrt(3)+1))/(sqrt(2)-sqrt(6))`


rationalize the denominator,


`=-((sqrt(6)+sqrt(2))(sqrt(2)+sqrt(6)))/((sqrt(2)-sqrt(6))(sqrt(2)+sqrt(6)))`


`=-(2sqrt(3)+6+2+2sqrt(3))/(2-6)`


`=-(4sqrt(3)+8)/(-4)`


`=sqrt(3)+2`

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