2/5除以（-2又2/5）-8/21*（-1又3/4）-0.75
=(2/5)÷(-12/5) - (8/21)*(-7/4) - 3/4
=(2/5)×(5/12) + (2/3) - (3/4)
=1/6 + (8/12) - (9/12)
=2/12 - 1/12
=1/12
25x3/4-（-25）x1/2+25x（-1/4）
=25×(3/4 + 1/2 - 1/4)
=25×1
=25
1/【（-2）的平方x0.5的平方-（-2.24）/（-2）的3次方】-1又7/18
=1/(4×0.25 - 2.24÷8) - 1又7/18
=1/(1 - 0.28) - 1又7/18
=1/0.72 - 1又7/18
=1/(18/25) - 1又7/18
=25/18 - 25/18
=0
-（-1/3）的3次方-【-1+（1-0.2x1又2/3)] / (-2)的2次方
=1/27 - (-1 +1 - 0.2×5/3)/4
=1/27 + (1/3)/4
=1/27 + 1/12
=4/108 + 9/108
=12/108