1.(x+2)(x+3)=x^2+3x+3x+6=x^2+6x+6
3,(x-3y)(x+y)=x^2+xy-3xy-3y^2=x^2-3y^2
5,(5x-3y)(4x+y)=20x^2+5xy-12xy-3y^2=20x^2-7xy-3y^2
7,(2a+1)(2a+2+b)=4a^2+4a+2ab+2a+2+b=4a^2+2ab+6a+b
9,-(2x-5)(x+2)=-2x^2-4x+5x+10=2x^2+x+10
11,2x^2+(x+7)(x-3)=2x^2+x^2-3x+7x-21=3x^2+4x-21
13,(x-5)(x+7)-x^2+2=x^2+7x-5x-35-x^2+2=2x-37
15,(x+1)(2x+3)+(3x+2)(x-4)=2x^2+3x+2x+3+3x^2-12x+2x-8=5x^2-5x-5
17,-(x-3)(x+4)+(x+2)(1-2x)=-x^2-4x+3x+12+x-2x^2+2-4x=-3x^2-4x+14
19,-3x^2+(x-1)(x+3)=-3x^2+x^2+3x-x-3=-2x^2+2x-3
21,5x^2-(2x+1)(x-2)=5x^2-2x^2-4x+x-2=3x^2-3x-2