将a=3,b=三分之一,c=三分之二分别代入代数式
2a-b-c
=2×3-1/3-2/3
=6-(1/3+2/3)
=6-1
=5
a+b-2c
=3+1/3-2×2/3
=3+1/3-4/3
=3+(-4/3+1/3)
=3-1
=2