利用和（差）角公式求下列各三角函数的值.

1、
原式=cos(-3*π+11π/12)
=cos(11π/12)
=cos(π/4+2π/3)
=cosπ/4cos2π/3-sinπ/4sin2π/3
=-(√6+√2)/4
2、
原式=tan(3π-π/12)
=tan(-π/12)
=tan(π/4-π/3)
=(tanπ/4-tanπ/3)/(1+tanπ/4tanπ/3)
=-2+√3