How do you add #(x^2-x)/(x^2+9x-10) + 3/(x+10)#?
The most importante thing is that you need to have all the parcels with the same denominator:
You easily can see that -10 is a zero of both
Knowing that a=10, we deduce that b=-1, because 10-1=9 and 10*(-1)=-10.
But -1 is not only a zero of
Ultimately, you have: