Verified answer

(x^2-3x+2)+(3x^2+7x-10)-(x^2-3x-8)

=x^2-3x+2+3x^2+7x-10-x^2+3x+8 (when a negative sign is outside a bracket, when you open it you must change the signs.)

then you rearrange(not necessary but it makes life easier),

=x^2+3x^2-x^2-3x+7x+3x+2-10+8

then you do your normal addition and subtraction.

and you will eventually get (if i did not make any mistakes)

=3x^2+7x

how many x^2 have you got ? add the x^2 terms together

how many x ditto ? add the x terms together

finally add the numbers together.

It's just a matter of "tidying up"

like 2 of something + 3 of something is just 5 of something.