(2) (2a-3)-3 (7-a) = 2a-3-21+3a = 5a-24 (note: remove the brackets first, and then merge similar items).

(3) 3 (1-a)-2 (a-1)-4 (-a) = 3-3a-2a+2-4+4a =1-a (Note: remove the brackets first, and then merge similar items).

(4) 2x-[-3y-3 (3x-3y)] = 2x-[-3y-9x+9y] = 2x-6y+9x =11x-6y (Note: open the brackets first.

(5)3(2x^2-y^2)-2(3y^2-2x^2)=6x^2-3y^2-6y^2+4x^2= 10x^2-9y^2

(Note: Open brackets first, then merge similar items)

(6)5x^2-[x^2+(5x^2-2x)-2(x^2-3x)]=5x^2-[x^2+5x^2-2x-2x^2+6x]=5x^2-[4x^2+4x)

=5x^2-4x^2-4x=x^2-4x

(Note: Open brackets first, then merge similar items)

(7) 2 (3a- 1)-3 (2-5a+3a 2), where a=- 1/3.

= 6a-2-6+15a-9a2 = 21a-8-9a2 (replace a =-1/3) = 21* (1/3)-8-. 2a^2-2-(a^2- 1/3b^2)+3/2(2/3a^2- 1/3b^2)= 1/2a^2-2-a^2+ 1/3b^2+a^2- 1/2b^2= 1/2a^2-2- 1/6b^2