中二數學題目 急急急!

1.
最大絕對誤差=2x1/2=1cm
上限=56+1=57cm
下限=56-1=55cm
2.
-178.439=-178.4(準確至最接近的10份1位)
3.
(ac+a)/b x (b^2-b)/(c+1)
=ab(c+1)(b-1) / b(c+1)
=a(b-1)
4.
3a^3/2m x 1/6a
=3a^3/12am
=a^2/4m
5.
(4c-ab)/(3ab-12c)
=(4c-ab)/3(ab-4c)
=-3
6.
3y/2m x 2ay/6a
=6ay^2/12am
=y^2/2m
7.
(a-6y)/(2a^2-12ay)
=(a-6y)/2a(a-6y)
=1/2a
8.
1/2a + 3/3a
=1/2a + 1/a
=1/2a + 2/2a
=3/2a
9.
6a/(3a-b) x 2b/(b-3a)
=-12ab(3a-b)^2
其他中間個乘號係唔係加號？如果係：
6a/(3a-b) + 2b/(b-3a)
=6a/(3a-b) - 2b/(3a-b)
=2(3a-b)/(3a-b)
=2
10.
4/(a+1) + b/(a-1)
=(4a-4+ab+b) / a^2-1