Steps
find the Least Common Multiple of the denominators (which is called the Least Common Denominator).
Change each fraction (using equivalent fractions) to make their denominators the same as the least common denominator.
Then add (or subtract) the fractions, as we wish!
your denominators stay the same so its 20
Because 3/6 is equal to 1/2.
You multiply the 1 (in 1/2) by 3, and the 2 (in 1/2) by 3 to get 3/6. You need to have a common denominator, and 6 was the common denominator.
Integrating gives
To compute the integral, substitute 
, so that 
. Then
Since 
for all 
, we can drop the absolute value, so we end up with
Given that 
, we have
so that
