2cosπ/2-tanπ/4+3/4tan²π/6-sinπ/6+cos²π/6+sin3π/2 -1/4cosπ
=2×0-1+3/4×(√3/3)²-1/2+(√3/2)²+(-1)-1/4×(-1)
=0-1+1/4-1/2+3/4-1+1/4
=-5/4