(2a^2+3ab-b^2)-(-3a^2+ab+5b^2)=5a^2+_____--6b^2
(2a^2+3ab-b^2)-(-3a^2+ab+5b^2)
=2a^2+3ab-b^2+3a^2-ab-5b^2
=5a^2+2ab-6b^2
____是2ab