=1-0.5×1/3×（2-9）=1-1/2×1/3×（-7）=1+7/6=13/6=2.17
1-(1-0.5)×⅓×[2-(-3)²] =1-0.5x⅓x(2-6)=1-1/6x(-4)=1+2/3=5/3
