-(-(-(-(a)))), a это = -50; 9,09; -20 10/13

 a(a + 5b) - (a + b)(a - b)=a^2+5ab-a^2+b^2=5ab+b^2b(3a-b) - (a - b)(a + b)=3ab-b^2-a^2+b^2=3ab-a^2 (y+10)(y-2)-4y(2 - 3y)=y^2+8y-20-8y+12y^2=13y^2-20 (a-4)(a+9)-5a(1-2a)=a^2+5a-36-5a+10a^2=11a^2-36 (2b-3)(3b+2)-3b(2b+3)=6b^2-9b+4b-6-6b^2-9b=-14b-6 (3a-1)(2a-3)-2a(3a+5)=6a^2-2a-6a+4-6a^2-10a=-18a+4(m+3)^2 -(m-2)(m+2)=m^2+6m+9-m^2+4=5m+13(a-1)^ - (a+1)(a-2)=a^2-2a+1-a^2-a-2=-3a-1(c+2)(c-3)-(c-1)^2=c^2-c-6-c^2+2c-1=c-7 (y-4)(y+4)-(y-3)^=y^2-16-y^2+6y-9=6y-25(a-2)(a+4)-(a+1)^  =a^2+2a-8-a^2-2a-1=-9(b-4)(b+2)-(b-1)^=b^2-2b-8-b^2+2b-1=-9