6a的2次方减5a(-a加2b-1)加4a(-3a-2分之5b-4分之3)=6a²+5a²-10ab+5a-12a²-10ab-3a=a²-20ab+2a
6a^2-5a*(-a+2b-1)+4a*(-3a-5b/2-3/4)=12a^2+5a^2-10ab+5a-12a^2-10ab-3a=5a^2-20ab+2a
