To express `1/((x+1)(x+2))` as partial fractions
Observe that the factors in the denominator are `(x+1)` and `(x+2)` . So, we can write:
`1/((x+1)(x+2))=A/(x+1)+B/(x+2)` where `A` and `B` are numbers.
We multiply both sides by the common denominator `(x+1)(x+2)` :
Note: if `x=-2, B=-1`
if `x=-1, A=1`
Putting these results together we have:
`=1/(x+1)-1/(x+2)` and we have expressed the given fraction in partial fractions.