cosπ/2,cos值表格

sinx cosx tanx的特殊值 比例cos2π/3=1这样的
cosπ/4=?
y=cos(1/2x π/4)①求增区间②求[-π.π]的值域③求在[-π.
tan(3π/2 α)dα=∫[sin(3π/2 α)d(3π/2 α)/ cos(3π/2 α)]=
已知sinα/2-cosα/2=-1/√5,且0 α π/2,求tanα/2的值