`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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