Answer:
Q1
|a-b| = b-a when a<b
Q2
104159/33000
Explanation:
Q1
If a<b then a-b will always be negative. To get the absolute value, we can take -(a-b) = -a+b = b-a.
Q2
Let x = 3.12789789789...
We isolate the repeating decimal to start after the decimal, so we multiply by 100.
100x = 312.789789789...
We want to multiply by 10 for each digit that repeats (in this case 3), to get the repeating part to the left of the decimal.
100000x = 312789.789789
Subtracting the two...
x(100000-100) = 312789.789789 - 312.789789
99900x = 312477
x = 312477/99000 = 104159/33000