Hi
As you can only add or substract item of the same nature, you must re organise terms.
so :
A = 15 a2 - 6ab- 8 a2+ 20 - 5ab - 31 + a2- ab
Here I have : " a²" ; "ab" then numbers.
In general, you start with letters with highest exponant. If two letters have the same exponent, use alphabetic order.
let's put order :
A = 15a²-8a²+a² -6ab-5ab -ab+20-31
Now you add or substract item of the same kind :
A = 8a² -12ab - 9
Here I can not do anything else, so calculus is over.
