答：
1）
21分之8÷(-7分之4)×(-1又2分之1)
=(8/21)×(-7/4)×(-1-1/2)
=-(2/3)×(-3/2)
=1
2）
(-1)²-(1-0.5)÷｛3分之1×【2-（-3）平方】｝
=1-0.5÷[(1/3)×(2-9)]
=1-(1/2)÷[(1/3)×(-7)]
=1-(1/2)÷(-7/3)
=1-(1/2)×(-3/7)
=1+3/14
=17/14